feat: pluggable storage backends (S3, Azure, local) with admin UI

Implement 4-phase external storage backends architecture:

Phase 1 - Foundation:
- BlobStorageBackend trait (application/ports/blob_storage_ports.rs)
- LocalBlobBackend: extracted all tokio::fs ops from DedupService
- S3BlobBackend: AWS SDK with custom endpoint support (MinIO, R2, B2)
- DedupService refactored to use Arc<dyn BlobStorageBackend>

Phase 2 - Admin Panel:
- StorageSettingsService with DB persistence + env override
- Storage tab in admin panel (backend selector, S3 form, provider presets)
- GET/PUT/POST endpoints for storage settings + connection test
- i18n keys (en/es) and BEM CSS

Phase 3 - Migration:
- MigrationBlobBackend decorator (dual-read: target-first + source fallback)
- Background migration job with parallel transfers + progress tracking
- Migration UI (progress bar, ETA, pause/resume/verify/complete)
- 6 admin API endpoints for migration lifecycle

Phase 4 - Enterprise Extras:
- CachedBlobBackend: LRU disk cache for remote backends
- EncryptedBlobBackend: AES-256-GCM at-rest encryption
- AzureBlobBackend: Azure Blob Storage support
- RetryBlobBackend: exponential backoff for transient errors
- Decorator composition in DI: retry → encryption → cache

All 223 tests passing, clippy clean, fmt verified.

Cargo.toml

@@ -58,6 +58,14 @@ dashmap = "6"
 socket2 = { version = "0.6.2", features = ["all"] }
 urlencoding = "2.1.3"
 utoipa = { version = "5", features = ["axum_extras", "uuid", "chrono"] }
+aws-sdk-s3 = "1"
+aws-config = { version = "1", features = ["behavior-version-latest"] }
+aws-smithy-types = "1"
+azure_core = "0.21"
+azure_storage = "0.21"
+azure_storage_blobs = "0.21"
+aes-gcm = "0.10"
+lru = "0.12"
 
 [features]
 default = []

TODO-STORAGE-BACKENDS.prompt.md

@@ -0,0 +1,867 @@
+# External Storage Backends — Implementation Plan
+
+> **Purpose**: This prompt provides Claude Code with full architectural context to implement pluggable blob storage backends (S3, Backblaze B2, MinIO, etc.) for OxiCloud, across 4 phases. All changes MUST respect the existing hexagonal architecture, BLAKE3 dedup system, and coding conventions defined in `CLAUDE.md`.
+
+---
+
+## Current Architecture Summary
+
+### How blobs are stored today
+
+- **Content-addressable**: Files hashed with BLAKE3 → stored at `.blobs/{2-char-prefix}/{hash}.blob`
+- **Dedup index**: PostgreSQL `storage.blobs` table (hash PK, ref_count, size, content_type)
+- **Write-first strategy**: Blob written to disk BEFORE PostgreSQL upsert (PG connection never held during disk I/O)
+- **Streaming reads**: 256 KB chunks via `tokio::fs::File` + `ReaderStream`
+- **Range support**: `AsyncSeekExt::seek()` + `file.take()` for HTTP Range requests
+
+### Key files
+
+| File | Role |
+|------|------|
+| `src/application/ports/dedup_ports.rs` | `DedupPort` trait — 12 methods, the hexagonal port |
+| `src/infrastructure/services/dedup_service.rs` | `DedupService` struct — sole implementation of `DedupPort` |
+| `src/common/di.rs` | `AppServiceFactory` — DI composition root, builds `DedupService` |
+| `src/common/config.rs` | `StorageConfig`, `AppConfig` — env var loading |
+| `src/interfaces/api/handlers/admin_handler.rs` | Admin API handlers (OIDC pattern to follow) |
+| `src/application/services/admin_settings_service.rs` | `AdminSettingsService` — runtime settings with env override |
+| `src/domain/repositories/settings_repository.rs` | `SettingsRepository` trait |
+| `src/infrastructure/repositories/pg/settings_pg_repository.rs` | PostgreSQL settings impl |
+| `static/admin.html` | Admin panel HTML (3 tabs: Dashboard, Users, OIDC) |
+| `static/js/views/admin/admin.js` | Admin panel JS logic |
+
+### DedupService filesystem operations (candidates for extraction)
+
+These are the EXACT `tokio::fs` calls inside `DedupService` that must be delegated to the new `BlobStorageBackend` trait:
+
+```
+initialize()        → fs::create_dir_all (blob_root, temp_root, 256 prefix dirs)
+store_from_file()   → fs::metadata, fs::try_exists, fs::rename, fs::copy, fs::remove_file
+read_blob_stream()  → File::open + ReaderStream
+read_blob_range_stream() → File::open + seek + take + ReaderStream
+blob_size()         → fs::metadata
+remove_reference()  → fs::remove_file (after PG commit)
+verify_integrity()  → spawn_blocking with path checks
+blob_path()         → PathBuf computation (sync)
+```
+
+### DedupService PostgreSQL operations (stay in DedupService, untouched)
+
+```
+store_from_file()   → INSERT … ON CONFLICT … RETURNING ref_count
+blob_exists()       → SELECT EXISTS from storage.blobs
+get_blob_metadata() → SELECT from storage.blobs
+add_reference()     → UPDATE ref_count + 1
+remove_reference()  → BEGIN TX → SELECT FOR UPDATE → DELETE if ref_count=0 → COMMIT
+get_stats()         → SELECT COUNT, SUM from storage.blobs
+verify_integrity()  → Streaming cursor SELECT from storage.blobs
+```
+
+---
+
+## Phase 1 — Foundation (Backend Trait + Local + S3)
+
+### Task 1.1: Create `BlobStorageBackend` trait
+
+**File**: `src/application/ports/blob_storage_ports.rs` (NEW)
+
+Create a minimal trait that abstracts ONLY raw byte I/O operations:
+
+```rust
+use async_trait::async_trait;
+use bytes::Bytes;
+use futures::Stream;
+use std::path::Path;
+use std::pin::Pin;
+use crate::domain::errors::DomainError;
+
+/// Health check result for storage backend connectivity
+#[derive(Debug, Clone, serde::Serialize)]
+pub struct StorageHealthStatus {
+    pub connected: bool,
+    pub backend_type: String,
+    pub message: String,
+    /// Optional: available space in bytes (if backend reports it)
+    pub available_bytes: Option<u64>,
+}
+
+/// Minimal trait for blob byte I/O — decoupled from dedup logic.
+///
+/// Implementations: `LocalBlobBackend`, `S3BlobBackend`, etc.
+/// DedupService owns an `Arc<dyn BlobStorageBackend>` and delegates
+/// all filesystem/object-store operations through this trait.
+#[async_trait]
+pub trait BlobStorageBackend: Send + Sync + 'static {
+    /// Initialize the backend (create directories, verify bucket access, etc.)
+    async fn initialize(&self) -> Result<(), DomainError>;
+
+    /// Store a blob from a local temporary file.
+    /// The backend MUST handle the case where the blob already exists (idempotent).
+    /// Returns the number of bytes stored.
+    async fn put_blob(&self, hash: &str, source_path: &Path) -> Result<u64, DomainError>;
+
+    /// Stream the full blob content.
+    async fn get_blob_stream(
+        &self,
+        hash: &str,
+    ) -> Result<Pin<Box<dyn Stream<Item = Result<Bytes, std::io::Error>> + Send>>, DomainError>;
+
+    /// Stream a byte range of the blob (for HTTP Range requests).
+    async fn get_blob_range_stream(
+        &self,
+        hash: &str,
+        start: u64,
+        end: Option<u64>,
+    ) -> Result<Pin<Box<dyn Stream<Item = Result<Bytes, std::io::Error>> + Send>>, DomainError>;
+
+    /// Delete a blob by hash. Must be idempotent (no error if already deleted).
+    async fn delete_blob(&self, hash: &str) -> Result<(), DomainError>;
+
+    /// Check if a blob exists in the backend.
+    async fn blob_exists(&self, hash: &str) -> Result<bool, DomainError>;
+
+    /// Get blob size in bytes without downloading content.
+    async fn blob_size(&self, hash: &str) -> Result<u64, DomainError>;
+
+    /// Verify connectivity and permissions. Used by admin "Test Connection" button.
+    async fn health_check(&self) -> Result<StorageHealthStatus, DomainError>;
+
+    /// Return the backend type name (for display in admin panel).
+    fn backend_type(&self) -> &'static str;
+}
+```
+
+Register in `src/application/ports/mod.rs` and `src/application/mod.rs`.
+
+### Task 1.2: Create `LocalBlobBackend`
+
+**File**: `src/infrastructure/services/local_blob_backend.rs` (NEW)
+
+Extract ALL `tokio::fs` operations from `DedupService` into this struct. This is a **pure refactor** — zero behavior change.
+
+```rust
+pub struct LocalBlobBackend {
+    blob_root: PathBuf,
+    temp_root: PathBuf,
+}
+```
+
+Methods to implement from the trait, mapping from current DedupService code:
+
+| Trait method | Source in DedupService | Key logic |
+|---|---|---|
+| `initialize()` | `DedupService::initialize()` lines 115-154 | Create `.blobs/`, `.dedup_temp/`, 256 prefix dirs |
+| `put_blob()` | `DedupService::store_from_file()` lines 196-253 | `fs::try_exists` → `fs::rename` (EXDEV fallback `fs::copy`) → cleanup source |
+| `get_blob_stream()` | `DedupService::read_blob_stream()` lines 306-323 | `File::open` → `ReaderStream::with_capacity(256KB)` |
+| `get_blob_range_stream()` | `DedupService::read_blob_range_stream()` lines 325-353 | `File::open` → `seek` → `take` → `ReaderStream` |
+| `delete_blob()` | `DedupService::remove_reference()` line ~469 | `fs::remove_file` |
+| `blob_exists()` | New (was inline `fs::try_exists`) | `fs::try_exists(blob_path)` |
+| `blob_size()` | `DedupService::blob_size()` lines 355-369 | `fs::metadata().len()` |
+| `health_check()` | New | Check blob_root is writable, return disk available via `statvfs` |
+| `backend_type()` | New | Return `"local"` |
+
+Also add a public helper:
+```rust
+pub fn blob_path(&self, hash: &str) -> PathBuf {
+    let prefix = &hash[..2];
+    self.blob_root.join(prefix).join(format!("{hash}.blob"))
+}
+```
+
+Register in `src/infrastructure/services/mod.rs`.
+
+### Task 1.3: Refactor `DedupService` to use `BlobStorageBackend`
+
+**File**: `src/infrastructure/services/dedup_service.rs` (MODIFY)
+
+Changes:
+1. Add field: `backend: Arc<dyn BlobStorageBackend>`
+2. Remove fields: `blob_root: PathBuf`, `temp_root: PathBuf` (moved to `LocalBlobBackend`)
+3. Update constructor to accept `Arc<dyn BlobStorageBackend>` instead of `storage_root: &Path`
+4. Replace all direct `tokio::fs` calls with `self.backend.*` calls
+5. Keep `blob_path()` in DedupPort as a delegation: `self.backend.blob_path()` — BUT since `blob_path()` returns `PathBuf` and is used by thumbnails/caching services, consider adding it to the backend trait OR keeping a separate method. For S3 backends, this should return a virtual path or the method should be deprecated in favor of streaming.
+
+**Critical**: `hash_file()` stays in `DedupService` (BLAKE3 hashing is NOT a backend concern — it always runs on local temp files before upload).
+
+**Critical**: The write-first strategy is preserved:
+```
+1. hash_file() on local temp file
+2. self.backend.put_blob(hash, temp_path)    ← backend moves/uploads
+3. INSERT INTO storage.blobs … ON CONFLICT   ← PostgreSQL upsert
+```
+
+**Critical**: `remove_reference()` flow preserved:
+```
+1. BEGIN TX → SELECT FOR UPDATE → check ref_count
+2. If ref_count == 1 → DELETE FROM storage.blobs → COMMIT
+3. self.backend.delete_blob(hash)             ← after PG commit
+```
+
+### Task 1.4: Create `S3BlobBackend`
+
+**File**: `src/infrastructure/services/s3_blob_backend.rs` (NEW)
+
+**Dependency to add to `Cargo.toml`**:
+```toml
+aws-sdk-s3 = "1"
+aws-config = { version = "1", features = ["behavior-version-latest"] }
+aws-smithy-types = "1"           # For ByteStream
+```
+
+> Note: `aws-sdk-s3` is the official AWS SDK for Rust. It's compatible with ALL S3-compatible services (Backblaze B2, MinIO, Cloudflare R2, DigitalOcean Spaces, Wasabi) via custom endpoint configuration.
+
+```rust
+pub struct S3BlobBackend {
+    client: aws_sdk_s3::Client,
+    bucket: String,
+}
+```
+
+**S3 key scheme**: Same as local — `{2-char-prefix}/{hash}.blob` (e.g., `a3/a3c5f2e8d1…blob`)
+
+Method mapping:
+
+| Trait method | S3 operation |
+|---|---|
+| `initialize()` | `head_bucket()` to verify bucket exists + permissions |
+| `put_blob()` | `put_object()` with `Body::from_path(source_path)`. Check existence with `head_object()` first for idempotency |
+| `get_blob_stream()` | `get_object()` → `.body.into_async_read()` → `ReaderStream` |
+| `get_blob_range_stream()` | `get_object().range(format!("bytes={start}-{end}"))` → stream |
+| `delete_blob()` | `delete_object()` (already idempotent in S3) |
+| `blob_exists()` | `head_object()` — 200 = true, 404 = false |
+| `blob_size()` | `head_object()` → `.content_length()` |
+| `health_check()` | `head_bucket()` + `list_objects_v2(max_keys=1)` |
+| `backend_type()` | Return `"s3"` |
+
+**S3 Client construction**: Must support custom endpoints for non-AWS providers:
+
+```rust
+impl S3BlobBackend {
+    pub async fn new(config: &S3StorageConfig) -> Result<Self, DomainError> {
+        let mut s3_config_builder = aws_sdk_s3::config::Builder::new()
+            .region(aws_sdk_s3::config::Region::new(config.region.clone()))
+            .credentials_provider(
+                aws_sdk_s3::config::Credentials::new(
+                    &config.access_key,
+                    &config.secret_key,
+                    None, None, "oxicloud",
+                )
+            )
+            .behavior_version_latest();
+
+        if let Some(endpoint) = &config.endpoint_url {
+            s3_config_builder = s3_config_builder
+                .endpoint_url(endpoint)
+                .force_path_style(config.force_path_style);
+        }
+
+        let client = aws_sdk_s3::Client::from_conf(s3_config_builder.build());
+        Ok(Self { client, bucket: config.bucket.clone() })
+    }
+}
+```
+
+### Task 1.5: Add storage backend configuration
+
+**File**: `src/common/config.rs` (MODIFY)
+
+Add to existing `StorageConfig`:
+
+```rust
+#[derive(Debug, Clone)]
+pub enum StorageBackendType {
+    Local,
+    S3,
+}
+
+#[derive(Debug, Clone)]
+pub struct S3StorageConfig {
+    pub endpoint_url: Option<String>,    // OXICLOUD_S3_ENDPOINT_URL
+    pub bucket: String,                  // OXICLOUD_S3_BUCKET
+    pub region: String,                  // OXICLOUD_S3_REGION (default: "us-east-1")
+    pub access_key: String,              // OXICLOUD_S3_ACCESS_KEY
+    pub secret_key: String,              // OXICLOUD_S3_SECRET_KEY
+    pub force_path_style: bool,          // OXICLOUD_S3_FORCE_PATH_STYLE (default: false)
+}
+
+// Add to existing StorageConfig:
+pub struct StorageConfig {
+    pub root_dir: String,                // existing
+    pub chunk_size: usize,               // existing
+    pub parallel_threshold: usize,       // existing
+    pub trash_retention_days: u32,       // existing
+    pub max_upload_size: usize,          // existing
+    pub backend: StorageBackendType,     // NEW — OXICLOUD_STORAGE_BACKEND (default: "local")
+    pub s3: Option<S3StorageConfig>,     // NEW — populated when backend=s3
+}
+```
+
+**Env var loading** in `AppConfig::from_env()`:
+```
+OXICLOUD_STORAGE_BACKEND     → "local" | "s3" (default: "local")
+OXICLOUD_S3_ENDPOINT_URL     → Optional custom endpoint
+OXICLOUD_S3_BUCKET           → Required when backend=s3
+OXICLOUD_S3_REGION           → Default "us-east-1"
+OXICLOUD_S3_ACCESS_KEY       → Required when backend=s3
+OXICLOUD_S3_SECRET_KEY       → Required when backend=s3
+OXICLOUD_S3_FORCE_PATH_STYLE → Default false
+```
+
+### Task 1.6: Wire backend selection in DI
+
+**File**: `src/common/di.rs` (MODIFY)
+
+In `create_core_services()`, replace the current DedupService construction:
+
+```rust
+// Build storage backend based on config
+let blob_backend: Arc<dyn BlobStorageBackend> = match self.config.storage.backend {
+    StorageBackendType::Local => {
+        Arc::new(LocalBlobBackend::new(&self.storage_path))
+    }
+    StorageBackendType::S3 => {
+        let s3_config = self.config.storage.s3.as_ref()
+            .expect("S3 config required when backend=s3");
+        Arc::new(S3BlobBackend::new(s3_config).await?)
+    }
+};
+
+blob_backend.initialize().await?;
+
+let dedup_service = Arc::new(DedupService::new(
+    blob_backend.clone(),
+    db_pool.clone(),
+    maintenance_pool.clone(),
+));
+```
+
+### Task 1.7: Handle `blob_path()` deprecation path
+
+The `DedupPort::blob_path()` method returns a `PathBuf` and is used by:
+- Thumbnail generation service (needs local file access)
+- File content caching (moka cache)
+
+For S3 backends, `blob_path()` has no meaning. Solutions:
+1. **For thumbnails**: Change thumbnail service to accept a `Stream` instead of a `PathBuf`, OR download to a temp file first
+2. **For caching**: Cache already works with streams
+3. Keep `blob_path()` on `DedupPort` but make it return `Option<PathBuf>` (None for remote backends) — consumers must handle the None case
+
+Search for all callers of `blob_path()` and update them.
+
+### Task 1.8: Tests
+
+- Unit test `LocalBlobBackend` in isolation (mock filesystem with temp dirs)
+- Unit test `S3BlobBackend` with a mock S3 (use `aws-smithy-runtime` test utilities or `mockall`)
+- Integration test: `DedupService` with `LocalBlobBackend` must pass ALL existing tests unchanged (this proves the refactor is correct)
+- Add `#[cfg(test)]` inline tests in each new file following existing project convention
+
+### Task 1.9: Pre-commit validation
+
+```bash
+cargo fmt --all
+cargo clippy -- -D warnings
+cargo test --workspace
+```
+
+ALL existing ~208 tests MUST pass. Zero regressions.
+
+---
+
+## Phase 2 — Admin Panel Configuration
+
+### Task 2.1: Storage settings service
+
+**File**: `src/application/services/storage_settings_service.rs` (NEW)
+
+Follow the EXACT same pattern as `AdminSettingsService` for OIDC. Create `StorageSettingsService`:
+
+```rust
+pub struct StorageSettingsService {
+    settings_repo: Arc<SettingsPgRepository>,
+    env_storage_config: StorageConfig,       // from AppConfig at startup
+}
+```
+
+**Methods** (follow OIDC pattern):
+
+| Method | Purpose |
+|---|---|
+| `get_storage_settings()` | Load from DB (category: `"storage"`), mask secrets, mark env overrides |
+| `save_storage_settings(dto, user_id)` | Upsert each field to `admin_settings`, mark secrets with `is_secret: true` |
+| `test_storage_connection(dto)` | Build temporary backend from DTO config, call `health_check()`, return result |
+| `load_effective_storage_config()` | Merge: DB settings + env var overrides + defaults |
+| `get_env_overrides()` | Return list of `OXICLOUD_S3_*` / `OXICLOUD_STORAGE_*` env vars that are set |
+
+**DB keys** (category: `"storage"`):
+
+```
+storage.backend              → "local" | "s3"
+storage.s3.endpoint_url      → string (optional)
+storage.s3.bucket            → string
+storage.s3.region            → string
+storage.s3.access_key        → string (is_secret: true)
+storage.s3.secret_key        → string (is_secret: true)
+storage.s3.force_path_style  → "true" | "false"
+```
+
+### Task 2.2: Storage admin API endpoints
+
+**File**: `src/interfaces/api/handlers/admin_handler.rs` (MODIFY)
+
+Add to `admin_routes()`:
+
+```rust
+.route("/settings/storage", get(get_storage_settings))
+.route("/settings/storage", put(save_storage_settings))
+.route("/settings/storage/test", post(test_storage_connection))
+```
+
+**Handler implementations** (follow OIDC handlers exactly):
+
+| Handler | Method | Body | Response |
+|---|---|---|---|
+| `get_storage_settings` | GET | — | `StorageSettingsDto` (secrets masked, env_overrides listed) |
+| `save_storage_settings` | PUT | `SaveStorageSettingsDto` | `{ "message": "Storage settings saved" }` |
+| `test_storage_connection` | POST | `TestStorageConnectionDto` | `StorageTestResultDto { connected, message, available_bytes }` |
+
+**DTOs** (add to `src/application/dtos/`):
+
+```rust
+#[derive(Serialize)]
+pub struct StorageSettingsDto {
+    pub backend: String,                     // "local" | "s3"
+    pub s3_endpoint_url: Option<String>,
+    pub s3_bucket: Option<String>,
+    pub s3_region: Option<String>,
+    pub s3_access_key_set: bool,             // masked — never send actual key
+    pub s3_secret_key_set: bool,             // masked — never send actual secret
+    pub s3_force_path_style: bool,
+    pub env_overrides: Vec<String>,          // which fields are locked by env vars
+    // Current stats
+    pub current_backend: String,
+    pub total_blobs: u64,
+    pub total_bytes_stored: u64,
+    pub dedup_ratio: f64,
+}
+
+#[derive(Deserialize)]
+pub struct SaveStorageSettingsDto {
+    pub backend: String,
+    pub s3_endpoint_url: Option<String>,
+    pub s3_bucket: Option<String>,
+    pub s3_region: Option<String>,
+    pub s3_access_key: Option<String>,       // only sent if changed
+    pub s3_secret_key: Option<String>,       // only sent if changed
+    pub s3_force_path_style: Option<bool>,
+}
+
+#[derive(Deserialize)]
+pub struct TestStorageConnectionDto {
+    pub backend: String,
+    pub s3_endpoint_url: Option<String>,
+    pub s3_bucket: Option<String>,
+    pub s3_region: Option<String>,
+    pub s3_access_key: Option<String>,
+    pub s3_secret_key: Option<String>,
+    pub s3_force_path_style: Option<bool>,
+}
+
+#[derive(Serialize)]
+pub struct StorageTestResultDto {
+    pub connected: bool,
+    pub message: String,
+    pub backend_type: String,
+    pub available_bytes: Option<u64>,
+}
+```
+
+### Task 2.3: Wire `StorageSettingsService` into DI
+
+**File**: `src/common/di.rs` (MODIFY)
+
+Add `StorageSettingsService` construction alongside `AdminSettingsService`. Add to `AppState`.
+
+### Task 2.4: Admin Panel — Storage tab (HTML)
+
+**File**: `static/admin.html` (MODIFY)
+
+Add a 4th tab button after the OIDC tab:
+
+```html
+<button class="admin-tab" id="tab-btn-storage">
+    <i class="fas fa-database"></i> <span data-i18n="admin.tab_storage">Storage</span>
+</button>
+```
+
+Add `tab-storage` content div with:
+
+1. **Backend selector** — Radio buttons: Local Filesystem / S3-Compatible
+2. **S3 configuration form** (shown/hidden based on selector):
+   - Provider preset dropdown (Amazon S3, Backblaze B2, Cloudflare R2, MinIO, DigitalOcean Spaces, Wasabi, Custom)
+   - Endpoint URL field
+   - Bucket field
+   - Region field
+   - Access Key ID field
+   - Secret Key field (password type)
+   - Force Path Style checkbox
+   - ENV badges on fields overridden by env vars (same as OIDC)
+3. **Test Connection button** → calls `POST /api/admin/settings/storage/test`
+4. **Save button** → calls `PUT /api/admin/settings/storage`
+5. **Current Status section**:
+   - Active backend type
+   - Total blobs / total size / dedup ratio (from `DedupStatsDto`)
+6. **Migration section** (Phase 3 — can be placeholder with "Coming soon")
+
+### Task 2.5: Admin Panel — Storage tab (JS)
+
+**File**: `static/js/views/admin/admin.js` (MODIFY)
+
+Follow OIDC tab patterns:
+
+```javascript
+// Provider presets
+const STORAGE_PRESETS = {
+    'aws':           { endpoint: '',                                  region: 'us-east-1',    pathStyle: false },
+    'backblaze':     { endpoint: 's3.{region}.backblazeb2.com',       region: 'us-west-004',  pathStyle: false },
+    'cloudflare-r2': { endpoint: '{accountId}.r2.cloudflarestorage.com', region: 'auto',      pathStyle: true  },
+    'minio':         { endpoint: 'http://localhost:9000',             region: 'us-east-1',    pathStyle: true  },
+    'digitalocean':  { endpoint: '{region}.digitaloceanspaces.com',   region: 'nyc3',         pathStyle: false },
+    'wasabi':        { endpoint: 's3.{region}.wasabisys.com',         region: 'us-east-1',    pathStyle: false },
+    'custom':        { endpoint: '',                                  region: '',             pathStyle: false },
+};
+```
+
+Functions:
+- `loadStorage()` — `GET /api/admin/settings/storage` → populate form
+- `saveStorage()` — Collect form → `PUT /api/admin/settings/storage`
+- `testStorageConnection()` — Collect form → `POST /api/admin/settings/storage/test` → show result
+- `onPresetChange(preset)` — Auto-fill endpoint/region/pathStyle from preset
+- `toggleS3Form(visible)` — Show/hide S3 fields when backend radio changes
+
+### Task 2.6: i18n keys
+
+**Files**: `static/locales/*.json` (MODIFY at minimum `en.json` and `es.json`)
+
+Add translation keys for all new UI labels:
+```
+admin.tab_storage
+admin.storage_backend
+admin.storage_local
+admin.storage_s3
+admin.storage_provider_preset
+admin.storage_endpoint_url
+admin.storage_bucket
+admin.storage_region
+admin.storage_access_key
+admin.storage_secret_key
+admin.storage_path_style
+admin.storage_test_connection
+admin.storage_test_success
+admin.storage_test_failure
+admin.storage_save
+admin.storage_saved
+admin.storage_current_status
+admin.storage_total_blobs
+admin.storage_total_size
+admin.storage_dedup_ratio
+admin.storage_migration
+admin.storage_migration_coming_soon
+```
+
+### Task 2.7: CSS for storage tab
+
+**File**: `static/css/admin.css` (MODIFY)
+
+Add styles for:
+- `.storage-backend-selector` — Radio button group
+- `.storage-provider-presets` — Dropdown styling
+- `.storage-form` — Form fields (reuse existing OIDC form patterns)
+- `.storage-status-grid` — Stats display
+- BEM methodology, CSS custom properties for colors, no raw hex/rgb
+
+---
+
+## Phase 3 — Migration Between Backends
+
+### Task 3.1: `MigrationBlobBackend` wrapper
+
+**File**: `src/infrastructure/services/migration_blob_backend.rs` (NEW)
+
+A `BlobStorageBackend` decorator that enables zero-downtime migration between backends:
+
+```rust
+pub struct MigrationBlobBackend {
+    source: Arc<dyn BlobStorageBackend>,    // old backend (read fallback)
+    target: Arc<dyn BlobStorageBackend>,    // new backend (primary for writes)
+    state: Arc<RwLock<MigrationState>>,
+}
+
+pub struct MigrationState {
+    pub status: MigrationStatus,
+    pub total_blobs: u64,
+    pub migrated_blobs: u64,
+    pub migrated_bytes: u64,
+    pub failed_blobs: Vec<String>,          // hashes that failed
+    pub started_at: Option<chrono::DateTime<chrono::Utc>>,
+    pub completed_at: Option<chrono::DateTime<chrono::Utc>>,
+}
+
+pub enum MigrationStatus {
+    Idle,           // no migration in progress
+    Running,        // background job active
+    Paused,         // manually paused
+    Completed,      // all blobs migrated
+    Failed,         // unrecoverable error
+}
+```
+
+**Behavior**:
+
+| Operation | During Migration |
+|---|---|
+| `put_blob()` | Write to **target** only |
+| `get_blob_stream()` | Try **target** first → fallback to **source** (+ schedule lazy copy) |
+| `get_blob_range_stream()` | Same fallback strategy |
+| `delete_blob()` | Delete from **both** (best-effort on source) |
+| `blob_exists()` | Check **target** first, then **source** |
+| `blob_size()` | Check **target** first, then **source** |
+
+### Task 3.2: Background migration job
+
+**File**: `src/infrastructure/services/migration_job.rs` (NEW)
+
+```rust
+pub async fn run_migration(
+    source: Arc<dyn BlobStorageBackend>,
+    target: Arc<dyn BlobStorageBackend>,
+    pool: Arc<PgPool>,
+    state: Arc<RwLock<MigrationState>>,
+    concurrency: usize,              // default: 4 parallel transfers
+    bandwidth_limit: Option<u64>,    // bytes/sec, None = unlimited
+) -> Result<(), DomainError>
+```
+
+**Algorithm**:
+1. Query `SELECT hash, size FROM storage.blobs ORDER BY hash` with streaming cursor
+2. For each blob hash:
+   a. Check if already exists in target (`target.blob_exists(hash)`)
+   b. If not: stream from source → write to temp file → `target.put_blob(hash, temp)`
+   c. Update `MigrationState` counters
+   d. Respect bandwidth limit via `tokio::time::sleep` throttling
+3. Use `futures::stream::buffer_unordered(concurrency)` for parallel transfers
+4. On error: log, add to `failed_blobs`, continue (don't abort entire migration)
+
+### Task 3.3: Migration API endpoints
+
+**File**: `src/interfaces/api/handlers/admin_handler.rs` (MODIFY)
+
+Add to `admin_routes()`:
+
+```rust
+.route("/storage/migration", get(get_migration_status))
+.route("/storage/migration/start", post(start_migration))
+.route("/storage/migration/pause", post(pause_migration))
+.route("/storage/migration/resume", post(resume_migration))
+.route("/storage/migration/complete", post(complete_migration))
+```
+
+| Endpoint | Purpose |
+|---|---|
+| `GET /migration` | Return `MigrationState` (status, progress, ETA) |
+| `POST /migration/start` | Begin background migration from current → configured backend |
+| `POST /migration/pause` | Pause the background job |
+| `POST /migration/resume` | Resume paused migration |
+| `POST /migration/complete` | Finalize: switch primary backend, optionally clean up source |
+
+### Task 3.4: Migration UI in admin panel
+
+In the Storage tab's Migration section:
+
+1. **Start Migration button** (when backend config differs from active)
+2. **Progress bar**: `{migrated} / {total} blobs ({percent}%) — {bytes_migrated} transferred`
+3. **Estimated time remaining** (based on throughput)
+4. **Pause / Resume button**
+5. **Complete Migration button** (enabled only when 100% migrated)
+6. **Failed blobs list** (expandable, with retry button)
+7. **Status badge**: Idle / Running / Paused / Completed / Failed
+
+### Task 3.5: Integrity verification post-migration
+
+After migration completes (before `complete_migration`):
+1. Run `verify_integrity()` against the target backend
+2. Compare blob count in PG vs target backend
+3. Sample-verify N random blobs (download + BLAKE3 hash check)
+4. Show verification results in admin UI before allowing finalization
+
+---
+
+## Phase 4 — Enterprise Extras
+
+### Task 4.1: `CachedBlobBackend` — LRU local disk cache
+
+**File**: `src/infrastructure/services/cached_blob_backend.rs` (NEW)
+
+A `BlobStorageBackend` decorator for remote backends (S3, Azure) that caches hot blobs on local SSD:
+
+```rust
+pub struct CachedBlobBackend {
+    inner: Arc<dyn BlobStorageBackend>,       // S3 backend
+    cache_dir: PathBuf,                        // local cache directory
+    max_cache_bytes: u64,                      // configurable limit
+    index: Arc<RwLock<LruCache<String, CacheEntry>>>,
+    current_size: Arc<AtomicU64>,
+}
+
+struct CacheEntry {
+    size: u64,
+    last_accessed: Instant,
+}
+```
+
+**Behavior**:
+- **Reads**: Check local cache first → cache hit returns local file stream → cache miss downloads from inner backend, writes to cache, returns stream
+- **Writes**: `put_blob()` writes to inner backend AND local cache simultaneously
+- **Eviction**: LRU eviction when `current_size` exceeds `max_cache_bytes`
+- **Startup**: Scan cache directory to rebuild index
+
+**Configuration** (admin panel):
+```
+storage.cache.enabled          → "true" | "false"
+storage.cache.max_size_bytes   → u64 (default: 50 GB)
+storage.cache.path             → PathBuf (default: "{storage_root}/.cache")
+```
+
+**Env vars**:
+```
+OXICLOUD_STORAGE_CACHE_ENABLED=true
+OXICLOUD_STORAGE_CACHE_MAX_SIZE=53687091200    # 50 GB
+OXICLOUD_STORAGE_CACHE_PATH=/fast-ssd/oxicloud-cache
+```
+
+### Task 4.2: Client-side encryption (AES-256-GCM)
+
+**File**: `src/infrastructure/services/encrypted_blob_backend.rs` (NEW)
+
+Another `BlobStorageBackend` decorator that encrypts blobs before sending to the inner backend:
+
+```rust
+pub struct EncryptedBlobBackend {
+    inner: Arc<dyn BlobStorageBackend>,
+    encryption_key: [u8; 32],                  // AES-256 key
+}
+```
+
+**Dependency**: Add `aes-gcm = "0.10"` to Cargo.toml.
+
+**Behavior**:
+- `put_blob()`: Read source → encrypt with AES-256-GCM (random 96-bit nonce prepended) → write encrypted to temp → `inner.put_blob(hash, encrypted_temp)`
+- `get_blob_stream()`: `inner.get_blob_stream()` → decrypt stream → return plaintext stream
+- **CRITICAL**: BLAKE3 hash is computed on the PLAINTEXT (before encryption), so dedup still works across encrypted backends
+- **Nonce storage**: Prepend 12-byte nonce to each encrypted blob (total overhead: 28 bytes per blob — 12 nonce + 16 GCM tag)
+
+**Configuration** (admin panel):
+```
+storage.encryption.enabled     → "true" | "false"
+storage.encryption.key         → base64-encoded 32-byte key (is_secret: true)
+```
+
+**Key generation**: Provide an admin API endpoint `POST /api/admin/settings/storage/generate-key` that generates a cryptographically secure key and returns it once (user must save it).
+
+**WARNING in admin UI**: "If you lose the encryption key, all data in the storage backend is IRRECOVERABLY LOST. Back up this key securely."
+
+### Task 4.3: Azure Blob Storage backend
+
+**File**: `src/infrastructure/services/azure_blob_backend.rs` (NEW)
+
+**Dependency**: `azure_storage_blobs = "0.21"`, `azure_storage = "0.21"`
+
+Same `BlobStorageBackend` trait implementation targeting Azure Blob Storage:
+- Container = bucket equivalent
+- Blob key scheme: `{prefix}/{hash}.blob` (same as S3/local)
+- Authentication: Account Name + Account Key OR SAS token
+
+**Configuration**:
+```
+OXICLOUD_AZURE_ACCOUNT_NAME
+OXICLOUD_AZURE_ACCOUNT_KEY
+OXICLOUD_AZURE_CONTAINER
+OXICLOUD_AZURE_SAS_TOKEN         # alternative auth
+```
+
+### Task 4.4: Bandwidth throttling & retry policies
+
+Apply to all remote backends (S3, Azure):
+
+**Throttling**:
+- Configurable upload/download bandwidth limit per-backend
+- Implemented via `tokio::time::sleep` between chunks
+- Admin configurable: `storage.s3.max_upload_bandwidth`, `storage.s3.max_download_bandwidth`
+
+**Retry policy** (exponential backoff):
+```rust
+pub struct RetryPolicy {
+    pub max_retries: u32,           // default: 3
+    pub initial_backoff_ms: u64,    // default: 100
+    pub max_backoff_ms: u64,        // default: 10_000
+    pub backoff_multiplier: f64,    // default: 2.0
+}
+```
+
+Wrap remote backend calls with retry logic for transient errors (network timeouts, 500s, 503s).
+
+---
+
+## Architecture Invariants (MUST be preserved)
+
+1. **BLAKE3 hashing**: Always performed locally on temp files, never delegated to backend
+2. **PostgreSQL dedup index**: `storage.blobs` table remains the source of truth for ref_count, metadata
+3. **Write-first strategy**: Blob stored in backend BEFORE PostgreSQL upsert
+4. **Remove-after-commit**: Blob deleted from backend AFTER PostgreSQL transaction commits
+5. **Streaming reads**: All blob reads return `Pin<Box<dyn Stream>>`, never load full blob into memory
+6. **Zero framework deps in domain**: `BlobStorageBackend` trait lives in `application/ports/`, not infrastructure
+7. **DI via AppState**: All backends are `Arc`-wrapped and assembled in `common/di.rs`
+8. **Env var precedence**: `OXICLOUD_*` env vars always override DB-stored admin settings
+9. **Admin guard**: All storage admin endpoints require JWT with role `"admin"`
+10. **Existing tests**: All ~208 tests must pass after Phase 1 refactor
+
+## Backend Decorator Composition
+
+The backends compose as decorators. In `di.rs`, the assembly looks like:
+
+```rust
+// Phase 1: Base backend
+let base_backend: Arc<dyn BlobStorageBackend> = match config {
+    Local => Arc::new(LocalBlobBackend::new(...)),
+    S3 => Arc::new(S3BlobBackend::new(...).await?),
+    Azure => Arc::new(AzureBlobBackend::new(...).await?),
+};
+
+// Phase 4: Optional encryption layer
+let backend = if encryption_enabled {
+    Arc::new(EncryptedBlobBackend::new(base_backend, key))
+} else {
+    base_backend
+};
+
+// Phase 4: Optional cache layer (only for remote backends)
+let backend = if cache_enabled && !matches!(config, Local) {
+    Arc::new(CachedBlobBackend::new(backend, cache_config))
+} else {
+    backend
+};
+
+// Phase 3: Optional migration wrapper
+let backend = if migration_in_progress {
+    Arc::new(MigrationBlobBackend::new(old_backend, backend, state))
+} else {
+    backend
+};
+
+// Finally: DedupService uses the composed backend
+let dedup_service = Arc::new(DedupService::new(backend, pool, maintenance_pool));
+```
+
+This decorator pattern means each feature (encryption, caching, migration) is:
+- Independently testable
+- Independently toggleable
+- Zero overhead when disabled
+- Composable in any order

src/application/dtos/settings_dto.rs

@@ -128,3 +128,97 @@ pub struct DashboardStatsDto {
     pub users_over_quota: i64,
     pub registration_enabled: bool,
 }
+
+// ============================================================================
+// Storage Settings DTOs (Admin Panel)
+// ============================================================================
+
+/// Current storage settings returned to admin UI (secrets masked)
+#[derive(Debug, Serialize, Deserialize)]
+pub struct StorageSettingsDto {
+    /// Active backend type: "local" or "s3"
+    pub backend: String,
+    pub s3_endpoint_url: Option<String>,
+    pub s3_bucket: Option<String>,
+    pub s3_region: Option<String>,
+    /// True if an access key is configured (never reveals the actual value)
+    pub s3_access_key_set: bool,
+    /// True if a secret key is configured (never reveals the actual value)
+    pub s3_secret_key_set: bool,
+    pub s3_force_path_style: bool,
+    /// Field names overridden by environment variables (read-only in UI)
+    pub env_overrides: Vec<String>,
+    // ── Current stats ──
+    pub current_backend: String,
+    pub total_blobs: u64,
+    pub total_bytes_stored: u64,
+    pub dedup_ratio: f64,
+}
+
+/// Request body for saving storage settings from the admin panel
+#[derive(Debug, Serialize, Deserialize)]
+pub struct SaveStorageSettingsDto {
+    pub backend: String,
+    pub s3_endpoint_url: Option<String>,
+    pub s3_bucket: Option<String>,
+    pub s3_region: Option<String>,
+    /// Only update if provided and non-empty (None = keep existing)
+    pub s3_access_key: Option<String>,
+    /// Only update if provided and non-empty (None = keep existing)
+    pub s3_secret_key: Option<String>,
+    pub s3_force_path_style: Option<bool>,
+}
+
+/// Request body for testing a storage connection
+#[derive(Debug, Serialize, Deserialize)]
+pub struct TestStorageConnectionDto {
+    pub backend: String,
+    pub s3_endpoint_url: Option<String>,
+    pub s3_bucket: Option<String>,
+    pub s3_region: Option<String>,
+    pub s3_access_key: Option<String>,
+    pub s3_secret_key: Option<String>,
+    pub s3_force_path_style: Option<bool>,
+}
+
+/// Result of a storage connection test
+#[derive(Debug, Serialize, Deserialize)]
+pub struct StorageTestResultDto {
+    pub connected: bool,
+    pub message: String,
+    pub backend_type: String,
+    pub available_bytes: Option<u64>,
+}
+
+// ============================================================================
+// Migration DTOs (Admin Panel — Storage Migration)
+// ============================================================================
+
+/// Migration progress returned by `GET /api/admin/storage/migration`.
+/// Re-exports the `MigrationState` shape for the admin UI.
+#[derive(Debug, Serialize, Deserialize)]
+pub struct MigrationStateDto {
+    pub status: String,
+    pub total_blobs: u64,
+    pub migrated_blobs: u64,
+    pub migrated_bytes: u64,
+    pub failed_blobs: Vec<String>,
+    pub started_at: Option<String>,
+    pub completed_at: Option<String>,
+    /// Estimated throughput in bytes/sec (for UI ETA calculation).
+    pub throughput_bytes_per_sec: Option<f64>,
+}
+
+/// Request body for `POST /api/admin/storage/migration/start`.
+#[derive(Debug, Serialize, Deserialize)]
+pub struct StartMigrationDto {
+    /// How many blobs to copy in parallel (default: 4).
+    pub concurrency: Option<usize>,
+}
+
+/// Request body (empty) for `POST /api/admin/storage/migration/verify`.
+#[derive(Debug, Serialize, Deserialize)]
+pub struct VerifyMigrationDto {
+    /// Number of random blobs to sample-check (default: 100).
+    pub sample_size: Option<usize>,
+}

src/application/ports/blob_storage_ports.rs

@@ -0,0 +1,88 @@
+//! Blob Storage Backend Port — abstracts raw byte I/O for content-addressable storage.
+//!
+//! This trait decouples `DedupService` from any specific storage medium.
+//! Implementations include:
+//! - `LocalBlobBackend`  — local filesystem (default)
+//! - `S3BlobBackend`     — any S3-compatible service (AWS, Backblaze B2, MinIO, R2…)
+//!
+//! `DedupService` owns an `Arc<dyn BlobStorageBackend>` and delegates all
+//! byte-level I/O through this trait, keeping BLAKE3 hashing, ref-counting
+//! and PostgreSQL index logic in `DedupService` itself.
+
+use bytes::Bytes;
+use futures::Stream;
+use serde::Serialize;
+use std::future::Future;
+use std::path::{Path, PathBuf};
+use std::pin::Pin;
+
+use crate::domain::errors::DomainError;
+
+/// Boxed future alias used by [`BlobStorageBackend`] to keep the trait dyn-compatible.
+type BoxFut<'a, T> = Pin<Box<dyn Future<Output = T> + Send + 'a>>;
+
+/// Pinned boxed byte stream — the return type for blob reads.
+pub type BlobStream = Pin<Box<dyn Stream<Item = Result<Bytes, std::io::Error>> + Send>>;
+
+/// Health-check result returned by [`BlobStorageBackend::health_check`].
+#[derive(Debug, Clone, Serialize)]
+pub struct StorageHealthStatus {
+    /// Whether the backend is reachable and functional.
+    pub connected: bool,
+    /// Human-readable backend identifier (e.g. `"local"`, `"s3"`).
+    pub backend_type: String,
+    /// Descriptive status message.
+    pub message: String,
+    /// Available space in bytes, if the backend can report it.
+    pub available_bytes: Option<u64>,
+}
+
+/// Minimal trait for blob byte I/O — decoupled from dedup logic.
+///
+/// Every method operates on a *hash key* that uniquely identifies a blob.
+/// The backend is responsible for mapping the hash to its own addressing
+/// scheme (filesystem path, S3 key, etc.).
+///
+/// Returns boxed futures so the trait is dyn-compatible (`Arc<dyn BlobStorageBackend>`).
+pub trait BlobStorageBackend: Send + Sync + 'static {
+    /// Perform any one-time setup (create directories, verify bucket, etc.).
+    fn initialize(&self) -> BoxFut<'_, Result<(), DomainError>>;
+
+    /// Store a blob from a local temporary file.
+    ///
+    /// Must be **idempotent**: if the blob already exists the call succeeds
+    /// without overwriting.  Returns the number of bytes stored.
+    fn put_blob(&self, hash: &str, source_path: &Path) -> BoxFut<'_, Result<u64, DomainError>>;
+
+    /// Stream the full blob content in chunks.
+    fn get_blob_stream(&self, hash: &str) -> BoxFut<'_, Result<BlobStream, DomainError>>;
+
+    /// Stream a byte range of the blob (for HTTP Range requests / video seek).
+    fn get_blob_range_stream(
+        &self,
+        hash: &str,
+        start: u64,
+        end: Option<u64>,
+    ) -> BoxFut<'_, Result<BlobStream, DomainError>>;
+
+    /// Delete a blob by hash.  Must be **idempotent** (no error if already gone).
+    fn delete_blob(&self, hash: &str) -> BoxFut<'_, Result<(), DomainError>>;
+
+    /// Check if a blob exists in the backend.
+    fn blob_exists(&self, hash: &str) -> BoxFut<'_, Result<bool, DomainError>>;
+
+    /// Get blob size in bytes without downloading content.
+    fn blob_size(&self, hash: &str) -> BoxFut<'_, Result<u64, DomainError>>;
+
+    /// Verify connectivity and permissions (used by the admin "Test Connection" button).
+    fn health_check(&self) -> BoxFut<'_, Result<StorageHealthStatus, DomainError>>;
+
+    /// Return the backend type name for display (e.g. `"local"`, `"s3"`).
+    fn backend_type(&self) -> &'static str;
+
+    /// Return the local filesystem path for a blob, if available.
+    ///
+    /// Only meaningful for local-filesystem backends.  Remote backends
+    /// return `None`; callers that need a local file must stream + spool.
+    fn local_blob_path(&self, hash: &str) -> Option<PathBuf>;
+}

src/application/ports/mod.rs

@@ -1,4 +1,5 @@
 pub mod auth_ports;
+pub mod blob_storage_ports;
 pub mod cache_ports;
 pub mod calendar_ports;
 pub mod carddav_ports;

src/application/services/mod.rs

@@ -18,6 +18,7 @@ pub mod nextcloud_login_flow_service;
 pub mod recent_service;
 pub mod search_service;
 pub mod share_service;
+pub mod storage_settings_service;
 pub mod storage_usage_service;
 pub mod trash_service;
 pub mod wopi_lock_service;

src/application/services/storage_settings_service.rs

@@ -0,0 +1,337 @@
+use std::collections::HashMap;
+use std::sync::Arc;
+use uuid::Uuid;
+
+use crate::application::dtos::settings_dto::{
+    SaveStorageSettingsDto, StorageSettingsDto, StorageTestResultDto, TestStorageConnectionDto,
+};
+use crate::application::ports::blob_storage_ports::BlobStorageBackend;
+use crate::common::config::{S3StorageConfig, StorageConfig};
+use crate::common::errors::{DomainError, ErrorKind};
+use crate::domain::repositories::settings_repository::SettingsRepository;
+use crate::infrastructure::repositories::pg::SettingsPgRepository;
+use crate::infrastructure::services::dedup_service::DedupService;
+use crate::infrastructure::services::s3_blob_backend::S3BlobBackend;
+
+/// Storage settings service — manages storage backend configuration via the admin panel.
+///
+/// Configuration priority: **env vars > DB settings > defaults**.
+pub struct StorageSettingsService {
+    settings_repo: Arc<SettingsPgRepository>,
+    env_storage_config: StorageConfig,
+    dedup_service: Arc<DedupService>,
+}
+
+impl StorageSettingsService {
+    pub fn new(
+        settings_repo: Arc<SettingsPgRepository>,
+        env_storage_config: StorageConfig,
+        dedup_service: Arc<DedupService>,
+    ) -> Self {
+        Self {
+            settings_repo,
+            env_storage_config,
+            dedup_service,
+        }
+    }
+
+    /// Detect which storage fields are overridden by environment variables.
+    fn get_env_overrides(&self) -> Vec<String> {
+        let mut out = Vec::new();
+        let vars = [
+            ("OXICLOUD_STORAGE_BACKEND", "backend"),
+            ("OXICLOUD_S3_ENDPOINT_URL", "s3_endpoint_url"),
+            ("OXICLOUD_S3_BUCKET", "s3_bucket"),
+            ("OXICLOUD_S3_REGION", "s3_region"),
+            ("OXICLOUD_S3_ACCESS_KEY", "s3_access_key"),
+            ("OXICLOUD_S3_SECRET_KEY", "s3_secret_key"),
+            ("OXICLOUD_S3_FORCE_PATH_STYLE", "s3_force_path_style"),
+        ];
+        for (env_key, field_name) in &vars {
+            if std::env::var(env_key).is_ok() {
+                out.push(field_name.to_string());
+            }
+        }
+        out
+    }
+
+    /// Apply environment variable overrides on top of a config.
+    fn apply_env_overrides(&self, config: &mut StorageConfig) {
+        let e = &self.env_storage_config;
+        if std::env::var("OXICLOUD_STORAGE_BACKEND").is_ok() {
+            config.backend = e.backend.clone();
+        }
+        // S3 env overrides — only apply if S3 config exists in env
+        if let Some(env_s3) = &e.s3 {
+            let s3 = config.s3.get_or_insert_with(|| S3StorageConfig {
+                endpoint_url: None,
+                bucket: String::new(),
+                region: "us-east-1".to_string(),
+                access_key: String::new(),
+                secret_key: String::new(),
+                force_path_style: false,
+            });
+            if std::env::var("OXICLOUD_S3_ENDPOINT_URL").is_ok() {
+                s3.endpoint_url = env_s3.endpoint_url.clone();
+            }
+            if std::env::var("OXICLOUD_S3_BUCKET").is_ok() {
+                s3.bucket = env_s3.bucket.clone();
+            }
+            if std::env::var("OXICLOUD_S3_REGION").is_ok() {
+                s3.region = env_s3.region.clone();
+            }
+            if std::env::var("OXICLOUD_S3_ACCESS_KEY").is_ok() {
+                s3.access_key = env_s3.access_key.clone();
+            }
+            if std::env::var("OXICLOUD_S3_SECRET_KEY").is_ok() {
+                s3.secret_key = env_s3.secret_key.clone();
+            }
+            if std::env::var("OXICLOUD_S3_FORCE_PATH_STYLE").is_ok() {
+                s3.force_path_style = env_s3.force_path_style;
+            }
+        }
+    }
+
+    /// Load effective storage config: DB settings + env var overrides + defaults.
+    pub async fn load_effective_storage_config(&self) -> Result<StorageConfig, DomainError> {
+        let db: HashMap<String, String> = self.settings_repo.get_by_category("storage").await?;
+        let d = StorageConfig::default();
+
+        let backend = db
+            .get("storage.backend")
+            .map(|v| match v.as_str() {
+                "s3" => crate::common::config::StorageBackendType::S3,
+                "azure" => crate::common::config::StorageBackendType::Azure,
+                _ => crate::common::config::StorageBackendType::Local,
+            })
+            .unwrap_or(d.backend);
+
+        let s3 = {
+            let bucket = db.get("storage.s3.bucket").cloned().unwrap_or_default();
+            if bucket.is_empty() {
+                None
+            } else {
+                Some(S3StorageConfig {
+                    endpoint_url: db
+                        .get("storage.s3.endpoint_url")
+                        .cloned()
+                        .filter(|s| !s.is_empty()),
+                    bucket,
+                    region: db
+                        .get("storage.s3.region")
+                        .cloned()
+                        .unwrap_or_else(|| "us-east-1".to_string()),
+                    access_key: db.get("storage.s3.access_key").cloned().unwrap_or_default(),
+                    secret_key: db.get("storage.s3.secret_key").cloned().unwrap_or_default(),
+                    force_path_style: db
+                        .get("storage.s3.force_path_style")
+                        .and_then(|v| v.parse().ok())
+                        .unwrap_or(false),
+                })
+            }
+        };
+
+        let mut config = StorageConfig {
+            backend,
+            s3,
+            ..self.env_storage_config.clone()
+        };
+
+        self.apply_env_overrides(&mut config);
+        Ok(config)
+    }
+
+    /// Get storage settings for display in admin UI (secrets masked).
+    pub async fn get_storage_settings(&self) -> Result<StorageSettingsDto, DomainError> {
+        let db: HashMap<String, String> = self.settings_repo.get_by_category("storage").await?;
+
+        let has_access_key = db
+            .get("storage.s3.access_key")
+            .map(|s| !s.is_empty())
+            .unwrap_or(false)
+            || std::env::var("OXICLOUD_S3_ACCESS_KEY")
+                .map(|s| !s.is_empty())
+                .unwrap_or(false);
+
+        let has_secret_key = db
+            .get("storage.s3.secret_key")
+            .map(|s| !s.is_empty())
+            .unwrap_or(false)
+            || std::env::var("OXICLOUD_S3_SECRET_KEY")
+                .map(|s| !s.is_empty())
+                .unwrap_or(false);
+
+        let effective = self.load_effective_storage_config().await?;
+        let stats = self.dedup_service.get_stats().await;
+        let current_backend = self.dedup_service.backend().backend_type().to_string();
+
+        let backend_str = match effective.backend {
+            crate::common::config::StorageBackendType::Local => "local",
+            crate::common::config::StorageBackendType::S3 => "s3",
+            crate::common::config::StorageBackendType::Azure => "azure",
+        };
+
+        Ok(StorageSettingsDto {
+            backend: backend_str.to_string(),
+            s3_endpoint_url: effective.s3.as_ref().and_then(|s| s.endpoint_url.clone()),
+            s3_bucket: effective.s3.as_ref().map(|s| s.bucket.clone()),
+            s3_region: effective.s3.as_ref().map(|s| s.region.clone()),
+            s3_access_key_set: has_access_key,
+            s3_secret_key_set: has_secret_key,
+            s3_force_path_style: effective.s3.as_ref().is_some_and(|s| s.force_path_style),
+            env_overrides: self.get_env_overrides(),
+            current_backend,
+            total_blobs: stats.total_blobs,
+            total_bytes_stored: stats.total_bytes_stored,
+            dedup_ratio: stats.dedup_ratio,
+        })
+    }
+
+    /// Save storage settings to DB.
+    pub async fn save_storage_settings(
+        &self,
+        dto: SaveStorageSettingsDto,
+        updated_by: Uuid,
+    ) -> Result<(), DomainError> {
+        let cat = "storage";
+        let by = Some(updated_by);
+
+        self.settings_repo
+            .set("storage.backend", &dto.backend, cat, false, by)
+            .await?;
+
+        if let Some(ref v) = dto.s3_endpoint_url {
+            self.settings_repo
+                .set("storage.s3.endpoint_url", v, cat, false, by)
+                .await?;
+        }
+        if let Some(ref v) = dto.s3_bucket {
+            self.settings_repo
+                .set("storage.s3.bucket", v, cat, false, by)
+                .await?;
+        }
+        if let Some(ref v) = dto.s3_region {
+            self.settings_repo
+                .set("storage.s3.region", v, cat, false, by)
+                .await?;
+        }
+        if let Some(ref v) = dto.s3_access_key
+            && !v.is_empty()
+        {
+            self.settings_repo
+                .set("storage.s3.access_key", v, cat, true, by)
+                .await?;
+        }
+        if let Some(ref v) = dto.s3_secret_key
+            && !v.is_empty()
+        {
+            self.settings_repo
+                .set("storage.s3.secret_key", v, cat, true, by)
+                .await?;
+        }
+        if let Some(v) = dto.s3_force_path_style {
+            self.settings_repo
+                .set(
+                    "storage.s3.force_path_style",
+                    &v.to_string(),
+                    cat,
+                    false,
+                    by,
+                )
+                .await?;
+        }
+
+        tracing::info!("Storage settings saved by admin (backend={})", dto.backend);
+        Ok(())
+    }
+
+    /// Test a storage connection by building a temporary backend and calling health_check().
+    pub async fn test_storage_connection(
+        &self,
+        dto: TestStorageConnectionDto,
+    ) -> Result<StorageTestResultDto, DomainError> {
+        match dto.backend.as_str() {
+            "local" => {
+                // Test local backend health via the current dedup service backend
+                let status = self.dedup_service.backend().health_check().await?;
+                Ok(StorageTestResultDto {
+                    connected: status.connected,
+                    message: status.message,
+                    backend_type: "local".to_string(),
+                    available_bytes: status.available_bytes,
+                })
+            }
+            "s3" => {
+                let bucket = dto.s3_bucket.as_deref().unwrap_or_default();
+                if bucket.is_empty() {
+                    return Ok(StorageTestResultDto {
+                        connected: false,
+                        message: "S3 bucket name is required".to_string(),
+                        backend_type: "s3".to_string(),
+                        available_bytes: None,
+                    });
+                }
+
+                // Build a temporary S3 backend from the DTO values,
+                // falling back to existing DB/env config for missing fields.
+                let effective = self.load_effective_storage_config().await.ok();
+                let existing_s3 = effective.as_ref().and_then(|c| c.s3.as_ref());
+
+                let config = S3StorageConfig {
+                    endpoint_url: dto
+                        .s3_endpoint_url
+                        .clone()
+                        .or_else(|| existing_s3.and_then(|s| s.endpoint_url.clone())),
+                    bucket: bucket.to_string(),
+                    region: dto.s3_region.clone().unwrap_or_else(|| {
+                        existing_s3
+                            .map(|s| s.region.clone())
+                            .unwrap_or_else(|| "us-east-1".to_string())
+                    }),
+                    access_key: dto
+                        .s3_access_key
+                        .clone()
+                        .filter(|s| !s.is_empty())
+                        .unwrap_or_else(|| {
+                            existing_s3
+                                .map(|s| s.access_key.clone())
+                                .unwrap_or_default()
+                        }),
+                    secret_key: dto
+                        .s3_secret_key
+                        .clone()
+                        .filter(|s| !s.is_empty())
+                        .unwrap_or_else(|| {
+                            existing_s3
+                                .map(|s| s.secret_key.clone())
+                                .unwrap_or_default()
+                        }),
+                    force_path_style: dto
+                        .s3_force_path_style
+                        .unwrap_or_else(|| existing_s3.is_some_and(|s| s.force_path_style)),
+                };
+
+                let backend = S3BlobBackend::new(&config);
+                match backend.health_check().await {
+                    Ok(status) => Ok(StorageTestResultDto {
+                        connected: status.connected,
+                        message: status.message,
+                        backend_type: "s3".to_string(),
+                        available_bytes: status.available_bytes,
+                    }),
+                    Err(e) => Ok(StorageTestResultDto {
+                        connected: false,
+                        message: format!("Connection failed: {}", e),
+                        backend_type: "s3".to_string(),
+                        available_bytes: None,
+                    }),
+                }
+            }
+            other => Err(DomainError::new(
+                ErrorKind::InvalidInput,
+                "Storage",
+                format!("Unknown backend type: {}", other),
+            )),
+        }
+    }
+}

src/common/config.rs

@@ -211,6 +211,127 @@ pub struct StorageConfig {
     /// Maximum upload file size in bytes (default: 10 GB).
     /// Applied as a hard limit to WebDAV PUT and streaming uploads.
     pub max_upload_size: usize,
+    /// Which blob storage backend to use (`local`, `s3`, or `azure`).
+    pub backend: StorageBackendType,
+    /// S3-compatible backend configuration (used when `backend == S3`).
+    pub s3: Option<S3StorageConfig>,
+    /// Azure Blob Storage configuration (used when `backend == Azure`).
+    pub azure: Option<AzureStorageConfig>,
+    /// Local disk cache for remote backends.
+    pub cache: BlobCacheConfig,
+    /// Client-side encryption.
+    pub encryption: EncryptionConfig,
+    /// Retry policy for remote backends.
+    pub retry: RetryConfig,
+}
+
+/// Which blob storage backend to use.
+#[derive(Debug, Clone, Default, PartialEq, Eq)]
+pub enum StorageBackendType {
+    /// Local filesystem (default).
+    #[default]
+    Local,
+    /// Any S3-compatible object store (AWS, Backblaze B2, R2, MinIO, …).
+    S3,
+    /// Azure Blob Storage.
+    Azure,
+}
+
+/// Configuration for an S3-compatible blob storage backend.
+#[derive(Debug, Clone)]
+pub struct S3StorageConfig {
+    /// Custom endpoint URL (required for non-AWS providers).
+    pub endpoint_url: Option<String>,
+    /// S3 bucket name.
+    pub bucket: String,
+    /// AWS region (default: `us-east-1`).
+    pub region: String,
+    /// Access key ID.
+    pub access_key: String,
+    /// Secret access key.
+    pub secret_key: String,
+    /// Force path-style access (required for MinIO, R2, some providers).
+    pub force_path_style: bool,
+}
+
+/// Configuration for Azure Blob Storage.
+#[derive(Debug, Clone)]
+pub struct AzureStorageConfig {
+    /// Azure storage account name.
+    pub account_name: String,
+    /// Azure storage account key.
+    pub account_key: String,
+    /// Container name.
+    pub container: String,
+    /// Optional SAS token (alternative to account key).
+    pub sas_token: Option<String>,
+}
+
+/// LRU local disk cache configuration for remote blob backends.
+#[derive(Debug, Clone)]
+pub struct BlobCacheConfig {
+    /// Enable the LRU disk cache (only useful for remote backends).
+    pub enabled: bool,
+    /// Maximum cache size in bytes (default: 50 GB).
+    pub max_size_bytes: u64,
+    /// Cache directory path (default: `{root_dir}/.blob-cache`).
+    pub cache_path: Option<String>,
+}
+
+impl Default for BlobCacheConfig {
+    fn default() -> Self {
+        Self {
+            enabled: false,
+            max_size_bytes: 50 * 1024 * 1024 * 1024, // 50 GB
+            cache_path: None,
+        }
+    }
+}
+
+/// Client-side encryption configuration.
+#[derive(Debug, Clone)]
+pub struct EncryptionConfig {
+    /// Enable AES-256-GCM encryption for blobs at rest.
+    pub enabled: bool,
+    /// Base64-encoded 32-byte encryption key.
+    pub key_base64: Option<String>,
+}
+
+impl Default for EncryptionConfig {
+    #[allow(clippy::derivable_impls)]
+    fn default() -> Self {
+        Self {
+            enabled: false,
+            key_base64: None,
+        }
+    }
+}
+
+/// Retry policy configuration for remote backends.
+#[derive(Debug, Clone)]
+pub struct RetryConfig {
+    /// Enable retry with exponential backoff.
+    pub enabled: bool,
+    /// Maximum number of retry attempts.
+    pub max_retries: u32,
+    /// Initial backoff in milliseconds.
+    pub initial_backoff_ms: u64,
+    /// Maximum backoff in milliseconds.
+    pub max_backoff_ms: u64,
+    /// Backoff multiplier.
+    pub backoff_multiplier: f64,
+}
+
+impl Default for RetryConfig {
+    fn default() -> Self {
+        Self {
+            enabled: true,
+            max_retries: 3,
+            initial_backoff_ms: 100,
+            max_backoff_ms: 10_000,
+            backoff_multiplier: 2.0,
+        }
+    }
 }
 
 impl Default for StorageConfig {
@@ -227,6 +348,12 @@ impl Default for StorageConfig {
             parallel_threshold: 100 * 1024 * 1024, // 100 MB
             trash_retention_days: 30,              // 30 days
             max_upload_size: MAX_UPLOAD_SIZE,
+            backend: StorageBackendType::Local,
+            s3: None,
+            azure: None,
+            cache: BlobCacheConfig::default(),
+            encryption: EncryptionConfig::default(),
+            retry: RetryConfig::default(),
         }
     }
 }
@@ -828,6 +955,95 @@ impl AppConfig {
             config.storage.max_upload_size = val;
         }
 
+        // Storage backend selection
+        if let Ok(backend) = env::var("OXICLOUD_STORAGE_BACKEND") {
+            match backend.to_lowercase().as_str() {
+                "s3" => config.storage.backend = StorageBackendType::S3,
+                "azure" => config.storage.backend = StorageBackendType::Azure,
+                _ => config.storage.backend = StorageBackendType::Local,
+            }
+        }
+
+        // S3-compatible storage configuration
+        if config.storage.backend == StorageBackendType::S3 {
+            let bucket = env::var("OXICLOUD_S3_BUCKET").unwrap_or_default();
+            if bucket.is_empty() {
+                tracing::warn!("OXICLOUD_STORAGE_BACKEND=s3 but OXICLOUD_S3_BUCKET is not set");
+            }
+            config.storage.s3 = Some(S3StorageConfig {
+                endpoint_url: env::var("OXICLOUD_S3_ENDPOINT_URL").ok(),
+                bucket,
+                region: env::var("OXICLOUD_S3_REGION").unwrap_or_else(|_| "us-east-1".to_string()),
+                access_key: env::var("OXICLOUD_S3_ACCESS_KEY").unwrap_or_default(),
+                secret_key: env::var("OXICLOUD_S3_SECRET_KEY").unwrap_or_default(),
+                force_path_style: env::var("OXICLOUD_S3_FORCE_PATH_STYLE")
+                    .map(|v| v.parse::<bool>().unwrap_or(false))
+                    .unwrap_or(false),
+            });
+        }
+
+        // Azure Blob Storage configuration
+        if config.storage.backend == StorageBackendType::Azure {
+            let container = env::var("OXICLOUD_AZURE_CONTAINER").unwrap_or_default();
+            if container.is_empty() {
+                tracing::warn!(
+                    "OXICLOUD_STORAGE_BACKEND=azure but OXICLOUD_AZURE_CONTAINER is not set"
+                );
+            }
+            config.storage.azure = Some(AzureStorageConfig {
+                account_name: env::var("OXICLOUD_AZURE_ACCOUNT_NAME").unwrap_or_default(),
+                account_key: env::var("OXICLOUD_AZURE_ACCOUNT_KEY").unwrap_or_default(),
+                container,
+                sas_token: env::var("OXICLOUD_AZURE_SAS_TOKEN").ok(),
+            });
+        }
+
+        // Blob cache configuration
+        if let Ok(v) = env::var("OXICLOUD_STORAGE_CACHE_ENABLED") {
+            config.storage.cache.enabled = v.parse::<bool>().unwrap_or(false);
+        }
+        if let Ok(v) = env::var("OXICLOUD_STORAGE_CACHE_MAX_SIZE")
+            && let Ok(bytes) = v.parse::<u64>()
+        {
+            config.storage.cache.max_size_bytes = bytes;
+        }
+        if let Ok(v) = env::var("OXICLOUD_STORAGE_CACHE_PATH") {
+            config.storage.cache.cache_path = Some(v);
+        }
+
+        // Encryption configuration
+        if let Ok(v) = env::var("OXICLOUD_STORAGE_ENCRYPTION_ENABLED") {
+            config.storage.encryption.enabled = v.parse::<bool>().unwrap_or(false);
+        }
+        if let Ok(v) = env::var("OXICLOUD_STORAGE_ENCRYPTION_KEY") {
+            config.storage.encryption.key_base64 = Some(v);
+        }
+
+        // Retry configuration
+        if let Ok(v) = env::var("OXICLOUD_STORAGE_RETRY_ENABLED") {
+            config.storage.retry.enabled = v.parse::<bool>().unwrap_or(true);
+        }
+        if let Ok(v) = env::var("OXICLOUD_STORAGE_RETRY_MAX_RETRIES")
+            && let Ok(n) = v.parse::<u32>()
+        {
+            config.storage.retry.max_retries = n;
+        }
+        if let Ok(v) = env::var("OXICLOUD_STORAGE_RETRY_INITIAL_BACKOFF_MS")
+            && let Ok(n) = v.parse::<u64>()
+        {
+            config.storage.retry.initial_backoff_ms = n;
+        }
+        if let Ok(v) = env::var("OXICLOUD_STORAGE_RETRY_MAX_BACKOFF_MS")
+            && let Ok(n) = v.parse::<u64>()
+        {
+            config.storage.retry.max_backoff_ms = n;
+        }
+        if let Ok(v) = env::var("OXICLOUD_STORAGE_RETRY_BACKOFF_MULTIPLIER")
+            && let Ok(n) = v.parse::<f64>()
+        {
+            config.storage.retry.backoff_multiplier = n;
+        }
+
         // OIDC configuration
         if let Ok(v) = env::var("OXICLOUD_OIDC_ENABLED") {
             config.oidc.enabled = v.parse::<bool>().unwrap_or(false);

src/common/di.rs

@@ -2,10 +2,14 @@ use sqlx::PgPool;
 use std::path::PathBuf;
 use std::sync::Arc;
 
+use crate::application::ports::blob_storage_ports::BlobStorageBackend;
+use crate::common::config::StorageBackendType;
 use crate::infrastructure::db::DbPools;
 
 use crate::application::services::admin_settings_service::AdminSettingsService;
 use crate::application::services::auth_application_service::AuthApplicationService;
+use crate::application::services::storage_settings_service::StorageSettingsService;
+use crate::infrastructure::services::migration_blob_backend::MigrationState;
 
 use crate::application::ports::file_ports::FileUseCaseFactory;
 use crate::application::services::favorites_service::FavoritesService;
@@ -153,10 +157,110 @@ impl AppServiceFactory {
         );
         image_transcode_service.initialize().await?;
 
+        // Build blob storage backend based on configuration
+        let base_backend: Arc<dyn BlobStorageBackend> = match self.config.storage.backend {
+            StorageBackendType::S3 => {
+                let s3_config = self
+                    .config
+                    .storage
+                    .s3
+                    .as_ref()
+                    .expect("S3 config required when OXICLOUD_STORAGE_BACKEND=s3");
+                Arc::new(
+                    crate::infrastructure::services::s3_blob_backend::S3BlobBackend::new(s3_config),
+                )
+            }
+            StorageBackendType::Azure => {
+                let az_config = self
+                    .config
+                    .storage
+                    .azure
+                    .as_ref()
+                    .expect("Azure config required when OXICLOUD_STORAGE_BACKEND=azure");
+                Arc::new(
+                    crate::infrastructure::services::azure_blob_backend::AzureBlobBackend::new(
+                        az_config,
+                    ),
+                )
+            }
+            StorageBackendType::Local => Arc::new(
+                crate::infrastructure::services::local_blob_backend::LocalBlobBackend::new(
+                    &self.storage_path,
+                ),
+            ),
+        };
+
+        // Stack decorators: retry → encryption → cache (inner-to-outer)
+        let mut blob_backend: Arc<dyn BlobStorageBackend> = base_backend;
+
+        // Retry decorator (for remote backends)
+        if self.config.storage.retry.enabled
+            && self.config.storage.backend != StorageBackendType::Local
+        {
+            use crate::infrastructure::services::retry_blob_backend::{
+                RetryBlobBackend, RetryPolicy,
+            };
+            let policy = RetryPolicy {
+                max_retries: self.config.storage.retry.max_retries,
+                initial_backoff: std::time::Duration::from_millis(
+                    self.config.storage.retry.initial_backoff_ms,
+                ),
+                max_backoff: std::time::Duration::from_millis(
+                    self.config.storage.retry.max_backoff_ms,
+                ),
+                backoff_multiplier: self.config.storage.retry.backoff_multiplier,
+            };
+            blob_backend = Arc::new(RetryBlobBackend::new(blob_backend, policy));
+            tracing::info!("Blob storage retry decorator enabled");
+        }
+
+        // Encryption decorator
+        if self.config.storage.encryption.enabled {
+            use crate::infrastructure::services::encrypted_blob_backend::EncryptedBlobBackend;
+            let key_b64 = self
+                .config
+                .storage
+                .encryption
+                .key_base64
+                .as_ref()
+                .expect("OXICLOUD_STORAGE_ENCRYPTION_KEY required when encryption is enabled");
+            let key_bytes =
+                base64::Engine::decode(&base64::engine::general_purpose::STANDARD, key_b64)
+                    .expect("OXICLOUD_STORAGE_ENCRYPTION_KEY must be valid base64");
+            let key: [u8; 32] = key_bytes.try_into().expect(
+                "OXICLOUD_STORAGE_ENCRYPTION_KEY must be exactly 32 bytes (base64 of 32 bytes)",
+            );
+            blob_backend = Arc::new(EncryptedBlobBackend::new(blob_backend, &key));
+            tracing::info!("Blob storage encryption decorator enabled (AES-256-GCM)");
+        }
+
+        // Cache decorator (for remote backends only)
+        if self.config.storage.cache.enabled
+            && self.config.storage.backend != StorageBackendType::Local
+        {
+            use crate::infrastructure::services::cached_blob_backend::{
+                BlobCacheConfig as CacheCfg, CachedBlobBackend,
+            };
+            let cache_path = self
+                .config
+                .storage
+                .cache
+                .cache_path
+                .as_ref()
+                .map(std::path::PathBuf::from)
+                .unwrap_or_else(|| self.storage_path.join(".blob-cache"));
+            let cfg = CacheCfg {
+                cache_dir: cache_path,
+                max_cache_bytes: self.config.storage.cache.max_size_bytes,
+            };
+            blob_backend = Arc::new(CachedBlobBackend::new(blob_backend, &cfg));
+            tracing::info!("Blob storage LRU disk cache enabled");
+        }
+
         // Deduplication service — PRIMARY blob storage engine (PostgreSQL-backed index)
         let dedup_service = Arc::new(
             crate::infrastructure::services::dedup_service::DedupService::new(
-                &self.storage_path,
+                blob_backend,
                 db_pool.clone(),
                 maintenance_pool.clone(),
             ),
@@ -631,6 +735,8 @@ impl AppServiceFactory {
             auth_service: auth_services,
             nextcloud: nextcloud_services,
             admin_settings_service: None,
+            storage_settings_service: None,
+            migration_state: Arc::new(tokio::sync::RwLock::new(MigrationState::default())),
             trash_service,
             share_service,
             favorites_service,
@@ -700,6 +806,15 @@ impl AppServiceFactory {
 
             app_state.admin_settings_service = Some(admin_svc.clone());
 
+            // 9b-1b. Wire storage settings service (reuses same settings_repo)
+            let storage_settings_svc = Arc::new(StorageSettingsService::new(
+                settings_repo.clone(),
+                self.config.storage.clone(),
+                app_state.core.dedup_service.clone(),
+            ));
+            app_state.storage_settings_service = Some(storage_settings_svc);
+            tracing::info!("Storage settings service initialized");
+
             // 9b-2. Log whether system needs first-time admin setup
             if !admin_svc.is_system_initialized().await {
                 tracing::warn!("╔══════════════════════════════════════════════════════════╗");
@@ -928,6 +1043,8 @@ pub struct AppState {
     pub auth_service: Option<AuthServices>,
     pub nextcloud: Option<NextcloudServices>,
     pub admin_settings_service: Option<Arc<AdminSettingsService>>,
+    pub storage_settings_service: Option<Arc<StorageSettingsService>>,
+    pub migration_state: Arc<tokio::sync::RwLock<MigrationState>>,
     pub trash_service: Option<Arc<TrashService>>,
     pub share_service: Option<Arc<ShareService>>,
     pub favorites_service: Option<Arc<FavoritesService>>,

src/infrastructure/services/azure_blob_backend.rs

@@ -0,0 +1,302 @@
+//! Azure Blob Storage Backend — stores blobs in an Azure Storage container.
+//!
+//! Authenticates via Account Name + Account Key (or SAS token).
+//! Blob key scheme mirrors local/S3: `{2-char-prefix}/{hash}.blob`.
+
+use std::path::{Path, PathBuf};
+use std::pin::Pin;
+
+use azure_storage::StorageCredentials;
+use azure_storage_blobs::prelude::*;
+use bytes::Bytes;
+use futures::StreamExt;
+use tokio::fs;
+
+use crate::application::ports::blob_storage_ports::{
+    BlobStorageBackend, BlobStream, StorageHealthStatus,
+};
+use crate::common::config::AzureStorageConfig;
+use crate::domain::errors::{DomainError, ErrorKind};
+
+/// Azure Blob Storage backend.
+pub struct AzureBlobBackend {
+    container_client: ContainerClient,
+    container_name: String,
+}
+
+impl AzureBlobBackend {
+    /// Build a new Azure backend from configuration.
+    pub fn new(config: &AzureStorageConfig) -> Self {
+        let credentials = if let Some(ref sas) = config.sas_token {
+            StorageCredentials::sas_token(sas).expect("Invalid SAS token")
+        } else {
+            StorageCredentials::access_key(&config.account_name, config.account_key.clone())
+        };
+
+        let container_client = ClientBuilder::new(&config.account_name, credentials)
+            .container_client(&config.container);
+
+        Self {
+            container_client,
+            container_name: config.container.clone(),
+        }
+    }
+
+    /// Compute the blob name for a given hash.
+    fn blob_name(hash: &str) -> String {
+        let prefix = &hash[0..2];
+        format!("{prefix}/{hash}.blob")
+    }
+
+    /// Get a `BlobClient` for a given hash.
+    fn blob_client(&self, hash: &str) -> BlobClient {
+        self.container_client.blob_client(Self::blob_name(hash))
+    }
+}
+
+impl BlobStorageBackend for AzureBlobBackend {
+    fn initialize(
+        &self,
+    ) -> Pin<Box<dyn std::future::Future<Output = Result<(), DomainError>> + Send + '_>> {
+        Box::pin(async move {
+            // Verify container exists by getting its properties
+            self.container_client.get_properties().await.map_err(|e| {
+                DomainError::internal_error(
+                    "Azure",
+                    format!("Cannot access container '{}': {}", self.container_name, e),
+                )
+            })?;
+
+            tracing::info!(
+                "Azure blob backend initialized: container={}",
+                self.container_name
+            );
+            Ok(())
+        })
+    }
+
+    fn put_blob(
+        &self,
+        hash: &str,
+        source_path: &Path,
+    ) -> Pin<Box<dyn std::future::Future<Output = Result<u64, DomainError>> + Send + '_>> {
+        let hash = hash.to_owned();
+        let source_path = source_path.to_owned();
+        Box::pin(async move {
+            let client = self.blob_client(&hash);
+
+            // Check if blob already exists (idempotent)
+            if client.get_properties().await.is_ok() {
+                let file_size = fs::metadata(&source_path)
+                    .await
+                    .map_err(|e| {
+                        DomainError::internal_error(
+                            "Azure",
+                            format!("Failed to stat source file: {e}"),
+                        )
+                    })?
+                    .len();
+                let _ = fs::remove_file(&source_path).await;
+                return Ok(file_size);
+            }
+
+            // Read file and upload as block blob
+            let data = fs::read(&source_path).await.map_err(|e| {
+                DomainError::internal_error("Azure", format!("Failed to read source: {e}"))
+            })?;
+            let file_size = data.len() as u64;
+
+            client.put_block_blob(data).await.map_err(|e| {
+                DomainError::internal_error("Azure", format!("Failed to upload blob {hash}: {e}"))
+            })?;
+
+            let _ = fs::remove_file(&source_path).await;
+            Ok(file_size)
+        })
+    }
+
+    fn get_blob_stream(
+        &self,
+        hash: &str,
+    ) -> Pin<Box<dyn std::future::Future<Output = Result<BlobStream, DomainError>> + Send + '_>>
+    {
+        let hash = hash.to_owned();
+        Box::pin(async move {
+            let client = self.blob_client(&hash);
+
+            let mut result_data: Vec<u8> = Vec::new();
+            let mut stream = client.get().into_stream();
+
+            while let Some(response) = stream.next().await {
+                let response = response.map_err(|e| {
+                    DomainError::new(
+                        ErrorKind::NotFound,
+                        "Azure",
+                        format!("Failed to get blob {hash}: {e}"),
+                    )
+                })?;
+                let mut body = response.data;
+                while let Some(chunk) = body.next().await {
+                    let chunk = chunk.map_err(|e| {
+                        DomainError::internal_error("Azure", format!("Stream read error: {e}"))
+                    })?;
+                    result_data.extend_from_slice(&chunk);
+                }
+            }
+
+            let stream: BlobStream = Box::pin(futures::stream::once(async move {
+                Ok(Bytes::from(result_data))
+            }));
+            Ok(stream)
+        })
+    }
+
+    fn get_blob_range_stream(
+        &self,
+        hash: &str,
+        start: u64,
+        end: Option<u64>,
+    ) -> Pin<Box<dyn std::future::Future<Output = Result<BlobStream, DomainError>> + Send + '_>>
+    {
+        let hash = hash.to_owned();
+        Box::pin(async move {
+            let client = self.blob_client(&hash);
+
+            let range = match end {
+                Some(e) => azure_core::request_options::Range::new(start, e),
+                None => azure_core::request_options::Range::new(start, u64::MAX),
+            };
+
+            let mut result_data: Vec<u8> = Vec::new();
+            let mut stream = client.get().range(range).into_stream();
+
+            while let Some(response) = stream.next().await {
+                let response = response.map_err(|e| {
+                    DomainError::new(
+                        ErrorKind::NotFound,
+                        "Azure",
+                        format!("Failed to get blob range {hash}: {e}"),
+                    )
+                })?;
+                let mut body = response.data;
+                while let Some(chunk) = body.next().await {
+                    let chunk = chunk.map_err(|e| {
+                        DomainError::internal_error(
+                            "Azure",
+                            format!("Stream range read error: {e}"),
+                        )
+                    })?;
+                    result_data.extend_from_slice(&chunk);
+                }
+            }
+
+            let stream: BlobStream = Box::pin(futures::stream::once(async move {
+                Ok(Bytes::from(result_data))
+            }));
+            Ok(stream)
+        })
+    }
+
+    fn delete_blob(
+        &self,
+        hash: &str,
+    ) -> Pin<Box<dyn std::future::Future<Output = Result<(), DomainError>> + Send + '_>> {
+        let hash = hash.to_owned();
+        Box::pin(async move {
+            let client = self.blob_client(&hash);
+
+            // Azure delete is not fully idempotent — 404 is expected for missing blobs
+            match client.delete().await {
+                Ok(_) => Ok(()),
+                Err(e) => {
+                    // If 404, treat as success (idempotent)
+                    let status = e.as_http_error().map(|h| h.status());
+                    if status == Some(azure_core::StatusCode::NotFound) {
+                        Ok(())
+                    } else {
+                        Err(DomainError::internal_error(
+                            "Azure",
+                            format!("Failed to delete blob {hash}: {e}"),
+                        ))
+                    }
+                }
+            }
+        })
+    }
+
+    fn blob_exists(
+        &self,
+        hash: &str,
+    ) -> Pin<Box<dyn std::future::Future<Output = Result<bool, DomainError>> + Send + '_>> {
+        let hash = hash.to_owned();
+        Box::pin(async move {
+            let client = self.blob_client(&hash);
+            match client.get_properties().await {
+                Ok(_) => Ok(true),
+                Err(e) => {
+                    let status = e.as_http_error().map(|h| h.status());
+                    if status == Some(azure_core::StatusCode::NotFound) {
+                        Ok(false)
+                    } else {
+                        Err(DomainError::internal_error(
+                            "Azure",
+                            format!("Failed to check blob {hash}: {e}"),
+                        ))
+                    }
+                }
+            }
+        })
+    }
+
+    fn blob_size(
+        &self,
+        hash: &str,
+    ) -> Pin<Box<dyn std::future::Future<Output = Result<u64, DomainError>> + Send + '_>> {
+        let hash = hash.to_owned();
+        Box::pin(async move {
+            let client = self.blob_client(&hash);
+            let props = client.get_properties().await.map_err(|e| {
+                DomainError::new(
+                    ErrorKind::NotFound,
+                    "Azure",
+                    format!("Failed to stat blob {hash}: {e}"),
+                )
+            })?;
+            Ok(props.blob.properties.content_length)
+        })
+    }
+
+    fn health_check(
+        &self,
+    ) -> Pin<
+        Box<dyn std::future::Future<Output = Result<StorageHealthStatus, DomainError>> + Send + '_>,
+    > {
+        Box::pin(async move {
+            match self.container_client.get_properties().await {
+                Ok(_) => Ok(StorageHealthStatus {
+                    connected: true,
+                    backend_type: "azure".to_string(),
+                    message: format!("Azure container '{}' is accessible", self.container_name),
+                    available_bytes: None,
+                }),
+                Err(e) => Ok(StorageHealthStatus {
+                    connected: false,
+                    backend_type: "azure".to_string(),
+                    message: format!(
+                        "Azure container '{}' is not accessible: {}",
+                        self.container_name, e
+                    ),
+                    available_bytes: None,
+                }),
+            }
+        })
+    }
+
+    fn backend_type(&self) -> &'static str {
+        "azure"
+    }
+
+    fn local_blob_path(&self, _hash: &str) -> Option<PathBuf> {
+        None
+    }
+}

src/infrastructure/services/cached_blob_backend.rs

@@ -0,0 +1,472 @@
+//! `CachedBlobBackend` — LRU local-disk cache decorator for remote blob backends.
+//!
+//! Wraps any `BlobStorageBackend` (typically S3 or Azure) and transparently
+//! caches hot blobs on a local SSD.  Reads check the cache first; cache misses
+//! are fetched from the inner backend and written to the cache.  Writes go to
+//! the inner backend AND the local cache simultaneously.
+//!
+//! Eviction is LRU based on a configurable maximum disk budget.
+
+use std::path::{Path, PathBuf};
+use std::pin::Pin;
+use std::sync::Arc;
+use std::sync::atomic::{AtomicU64, Ordering};
+
+use lru::LruCache;
+use std::num::NonZeroUsize;
+use tokio::fs;
+use tokio::io::{AsyncReadExt, AsyncSeekExt, AsyncWriteExt};
+use tokio::sync::Mutex;
+use tokio_util::io::ReaderStream;
+
+use crate::application::ports::blob_storage_ports::{
+    BlobStorageBackend, BlobStream, StorageHealthStatus,
+};
+use crate::domain::errors::DomainError;
+
+/// Chunk size for streaming cached file reads (256 KB).
+const STREAM_CHUNK_SIZE: usize = 256 * 1024;
+
+// ── Configuration ──────────────────────────────────────────────────
+
+/// Configuration for the LRU disk cache.
+#[derive(Debug, Clone)]
+pub struct BlobCacheConfig {
+    /// Directory where cached blobs are stored.
+    pub cache_dir: PathBuf,
+    /// Maximum total cache size in bytes.
+    pub max_cache_bytes: u64,
+}
+
+// ── Cache entry ────────────────────────────────────────────────────
+
+#[derive(Debug, Clone)]
+struct CacheEntry {
+    size: u64,
+}
+
+// ── CachedBlobBackend ──────────────────────────────────────────────
+
+/// A `BlobStorageBackend` decorator that adds an LRU disk cache in front of
+/// a remote backend.
+pub struct CachedBlobBackend {
+    inner: Arc<dyn BlobStorageBackend>,
+    cache_dir: PathBuf,
+    max_cache_bytes: u64,
+    index: Arc<Mutex<LruCache<String, CacheEntry>>>,
+    current_size: Arc<AtomicU64>,
+}
+
+impl CachedBlobBackend {
+    /// Create a new cached backend wrapping `inner`.
+    pub fn new(inner: Arc<dyn BlobStorageBackend>, config: &BlobCacheConfig) -> Self {
+        Self {
+            inner,
+            cache_dir: config.cache_dir.clone(),
+            max_cache_bytes: config.max_cache_bytes,
+            // Capacity is essentially unbounded — eviction is by byte budget, not count.
+            index: Arc::new(Mutex::new(LruCache::new(
+                NonZeroUsize::new(1_000_000).unwrap(),
+            ))),
+            current_size: Arc::new(AtomicU64::new(0)),
+        }
+    }
+
+    /// Path where a blob is cached locally.
+    fn cached_path(&self, hash: &str) -> PathBuf {
+        let prefix = &hash[..2.min(hash.len())];
+        self.cache_dir.join(prefix).join(format!("{hash}.blob"))
+    }
+}
+
+impl BlobStorageBackend for CachedBlobBackend {
+    fn initialize(
+        &self,
+    ) -> Pin<Box<dyn std::future::Future<Output = Result<(), DomainError>> + Send + '_>> {
+        let inner = self.inner.clone();
+        let cache_dir = self.cache_dir.clone();
+        let index = self.index.clone();
+        let current_size = self.current_size.clone();
+        Box::pin(async move {
+            inner.initialize().await?;
+
+            // Create cache dir structure (256 prefix dirs)
+            fs::create_dir_all(&cache_dir).await.map_err(|e| {
+                DomainError::internal_error("BlobCache", format!("mkdir cache_dir: {e}"))
+            })?;
+
+            // Scan existing cache to rebuild index
+            let mut total_bytes = 0u64;
+            let mut idx = index.lock().await;
+            if let Ok(mut read_dir) = fs::read_dir(&cache_dir).await {
+                while let Ok(Some(prefix_entry)) = read_dir.next_entry().await {
+                    if !prefix_entry.path().is_dir() {
+                        continue;
+                    }
+                    if let Ok(mut sub_dir) = fs::read_dir(prefix_entry.path()).await {
+                        while let Ok(Some(entry)) = sub_dir.next_entry().await {
+                            let path = entry.path();
+                            if path.extension().and_then(|e| e.to_str()) == Some("blob")
+                                && let Some(stem) = path.file_stem().and_then(|s| s.to_str())
+                            {
+                                let size = fs::metadata(&path).await.map(|m| m.len()).unwrap_or(0);
+                                idx.put(stem.to_string(), CacheEntry { size });
+                                total_bytes += size;
+                            }
+                        }
+                    }
+                }
+            }
+            drop(idx);
+            current_size.store(total_bytes, Ordering::Relaxed);
+            tracing::info!(
+                "Blob cache initialized: {} bytes in cache at {}",
+                total_bytes,
+                cache_dir.display()
+            );
+            Ok(())
+        })
+    }
+
+    fn put_blob(
+        &self,
+        hash: &str,
+        source_path: &Path,
+    ) -> Pin<Box<dyn std::future::Future<Output = Result<u64, DomainError>> + Send + '_>> {
+        let inner = self.inner.clone();
+        let hash = hash.to_string();
+        let source = source_path.to_path_buf();
+        let self_ref = CachedRef {
+            cache_dir: self.cache_dir.clone(),
+            max_cache_bytes: self.max_cache_bytes,
+            index: self.index.clone(),
+            current_size: self.current_size.clone(),
+        };
+        Box::pin(async move {
+            // Write to inner backend
+            let bytes = inner.put_blob(&hash, &source).await?;
+            // Also cache locally (best-effort)
+            let _ = self_ref.insert_into_cache_static(&hash, &source).await;
+            Ok(bytes)
+        })
+    }
+
+    fn get_blob_stream(
+        &self,
+        hash: &str,
+    ) -> Pin<Box<dyn std::future::Future<Output = Result<BlobStream, DomainError>> + Send + '_>>
+    {
+        let hash = hash.to_string();
+        let cached = self.cached_path(&hash);
+        let index = self.index.clone();
+        let inner = self.inner.clone();
+        let cache_dir = self.cache_dir.clone();
+        let max_cache_bytes = self.max_cache_bytes;
+        let current_size = self.current_size.clone();
+        Box::pin(async move {
+            // Check cache
+            {
+                let mut idx = index.lock().await;
+                if idx.get(&hash).is_some() {
+                    if let Ok(file) = fs::File::open(&cached).await {
+                        let stream: BlobStream =
+                            Box::pin(ReaderStream::with_capacity(file, STREAM_CHUNK_SIZE));
+                        return Ok(stream);
+                    }
+                    // Cache entry stale — remove
+                    if let Some(entry) = idx.pop(&hash) {
+                        current_size.fetch_sub(entry.size, Ordering::Relaxed);
+                    }
+                }
+            }
+
+            // Cache miss — fetch from inner, spool to cache
+            let self_ref = CachedRef {
+                cache_dir,
+                max_cache_bytes,
+                index: index.clone(),
+                current_size: current_size.clone(),
+            };
+            let dest = self_ref.fetch_and_cache_static(&hash, &*inner).await?;
+            let file = fs::File::open(&dest).await.map_err(|e| {
+                DomainError::internal_error("BlobCache", format!("re-open cached: {e}"))
+            })?;
+            let stream: BlobStream = Box::pin(ReaderStream::with_capacity(file, STREAM_CHUNK_SIZE));
+            Ok(stream)
+        })
+    }
+
+    fn get_blob_range_stream(
+        &self,
+        hash: &str,
+        start: u64,
+        end: Option<u64>,
+    ) -> Pin<Box<dyn std::future::Future<Output = Result<BlobStream, DomainError>> + Send + '_>>
+    {
+        let hash = hash.to_string();
+        let cached = self.cached_path(&hash);
+        let index = self.index.clone();
+        let inner = self.inner.clone();
+        let cache_dir = self.cache_dir.clone();
+        let max_cache_bytes = self.max_cache_bytes;
+        let current_size = self.current_size.clone();
+        Box::pin(async move {
+            // Try cache first
+            {
+                let mut idx = index.lock().await;
+                if idx.get(&hash).is_some() {
+                    if let Ok(mut file) = fs::File::open(&cached).await {
+                        file.seek(std::io::SeekFrom::Start(start))
+                            .await
+                            .map_err(|e| {
+                                DomainError::internal_error("BlobCache", format!("seek: {e}"))
+                            })?;
+                        let take_len = end.map(|e| e - start + 1).unwrap_or(u64::MAX);
+                        let limited = file.take(take_len);
+                        let stream: BlobStream =
+                            Box::pin(ReaderStream::with_capacity(limited, STREAM_CHUNK_SIZE));
+                        return Ok(stream);
+                    }
+                    if let Some(entry) = idx.pop(&hash) {
+                        current_size.fetch_sub(entry.size, Ordering::Relaxed);
+                    }
+                }
+            }
+
+            // Cache miss — fetch full blob into cache, then serve range
+            let self_ref = CachedRef {
+                cache_dir,
+                max_cache_bytes,
+                index: index.clone(),
+                current_size: current_size.clone(),
+            };
+            let dest = self_ref.fetch_and_cache_static(&hash, &*inner).await?;
+            let mut file = fs::File::open(&dest)
+                .await
+                .map_err(|e| DomainError::internal_error("BlobCache", format!("re-open: {e}")))?;
+            file.seek(std::io::SeekFrom::Start(start))
+                .await
+                .map_err(|e| DomainError::internal_error("BlobCache", format!("seek: {e}")))?;
+            let take_len = end.map(|e| e - start + 1).unwrap_or(u64::MAX);
+            let limited = file.take(take_len);
+            let stream: BlobStream =
+                Box::pin(ReaderStream::with_capacity(limited, STREAM_CHUNK_SIZE));
+            Ok(stream)
+        })
+    }
+
+    fn delete_blob(
+        &self,
+        hash: &str,
+    ) -> Pin<Box<dyn std::future::Future<Output = Result<(), DomainError>> + Send + '_>> {
+        let inner = self.inner.clone();
+        let hash = hash.to_string();
+        let cached = self.cached_path(&hash);
+        let index = self.index.clone();
+        let current_size = self.current_size.clone();
+        Box::pin(async move {
+            inner.delete_blob(&hash).await?;
+            // Remove from cache
+            let mut idx = index.lock().await;
+            if let Some(entry) = idx.pop(&hash) {
+                current_size.fetch_sub(entry.size, Ordering::Relaxed);
+            }
+            let _ = fs::remove_file(&cached).await;
+            Ok(())
+        })
+    }
+
+    fn blob_exists(
+        &self,
+        hash: &str,
+    ) -> Pin<Box<dyn std::future::Future<Output = Result<bool, DomainError>> + Send + '_>> {
+        let inner = self.inner.clone();
+        let hash = hash.to_string();
+        let index = self.index.clone();
+        Box::pin(async move {
+            // Check cache first (fast)
+            {
+                let mut idx = index.lock().await;
+                if idx.get(&hash).is_some() {
+                    return Ok(true);
+                }
+            }
+            inner.blob_exists(&hash).await
+        })
+    }
+
+    fn blob_size(
+        &self,
+        hash: &str,
+    ) -> Pin<Box<dyn std::future::Future<Output = Result<u64, DomainError>> + Send + '_>> {
+        let inner = self.inner.clone();
+        let hash = hash.to_string();
+        let index = self.index.clone();
+        let cached = self.cached_path(&hash);
+        Box::pin(async move {
+            // Check cache
+            {
+                let mut idx = index.lock().await;
+                if let Some(entry) = idx.get(&hash) {
+                    return Ok(entry.size);
+                }
+            }
+            // Fallback to cached file on disk (in case index was lost)
+            if let Ok(meta) = fs::metadata(&cached).await {
+                return Ok(meta.len());
+            }
+            inner.blob_size(&hash).await
+        })
+    }
+
+    fn health_check(
+        &self,
+    ) -> Pin<
+        Box<dyn std::future::Future<Output = Result<StorageHealthStatus, DomainError>> + Send + '_>,
+    > {
+        let inner = self.inner.clone();
+        let cache_dir = self.cache_dir.clone();
+        let current_size = self.current_size.clone();
+        let max_bytes = self.max_cache_bytes;
+        Box::pin(async move {
+            let mut status = inner.health_check().await?;
+            let used = current_size.load(Ordering::Relaxed);
+            status.message = format!(
+                "{} | Cache: {}/{} bytes used at {}",
+                status.message,
+                used,
+                max_bytes,
+                cache_dir.display()
+            );
+            status.backend_type = format!("cached({})", status.backend_type);
+            Ok(status)
+        })
+    }
+
+    fn backend_type(&self) -> &'static str {
+        "cached"
+    }
+
+    fn local_blob_path(&self, hash: &str) -> Option<PathBuf> {
+        // If the blob is cached locally, return that path
+        let path = self.cached_path(hash);
+        if path.exists() { Some(path) } else { None }
+    }
+}
+
+// ── Helper struct for owned references in async closures ───────────
+
+/// Cloneable set of cache internals — avoids borrow issues in boxed futures.
+struct CachedRef {
+    cache_dir: PathBuf,
+    max_cache_bytes: u64,
+    index: Arc<Mutex<LruCache<String, CacheEntry>>>,
+    current_size: Arc<AtomicU64>,
+}
+
+impl CachedRef {
+    fn cached_path(&self, hash: &str) -> PathBuf {
+        let prefix = &hash[..2.min(hash.len())];
+        self.cache_dir.join(prefix).join(format!("{hash}.blob"))
+    }
+
+    async fn insert_into_cache_static(
+        &self,
+        hash: &str,
+        source_path: &Path,
+    ) -> Result<(), DomainError> {
+        let dest = self.cached_path(hash);
+        if let Some(parent) = dest.parent() {
+            fs::create_dir_all(parent).await.map_err(|e| {
+                DomainError::internal_error("BlobCache", format!("mkdir failed: {e}"))
+            })?;
+        }
+
+        let size = fs::metadata(source_path)
+            .await
+            .map(|m| m.len())
+            .unwrap_or(0);
+
+        fs::copy(source_path, &dest).await.map_err(|e| {
+            DomainError::internal_error("BlobCache", format!("cache copy failed: {e}"))
+        })?;
+
+        let mut idx = self.index.lock().await;
+        if let Some(old) = idx.put(hash.to_string(), CacheEntry { size }) {
+            self.current_size.fetch_sub(old.size, Ordering::Relaxed);
+        }
+        self.current_size.fetch_add(size, Ordering::Relaxed);
+
+        while self.current_size.load(Ordering::Relaxed) > self.max_cache_bytes {
+            if let Some((evicted_hash, evicted_entry)) = idx.pop_lru() {
+                self.current_size
+                    .fetch_sub(evicted_entry.size, Ordering::Relaxed);
+                let evicted_path = self.cached_path(&evicted_hash);
+                let _ = fs::remove_file(&evicted_path).await;
+            } else {
+                break;
+            }
+        }
+        Ok(())
+    }
+
+    async fn fetch_and_cache_static(
+        &self,
+        hash: &str,
+        inner: &dyn BlobStorageBackend,
+    ) -> Result<PathBuf, DomainError> {
+        let stream = inner.get_blob_stream(hash).await?;
+
+        let dest = self.cached_path(hash);
+        if let Some(parent) = dest.parent() {
+            fs::create_dir_all(parent).await.map_err(|e| {
+                DomainError::internal_error("BlobCache", format!("mkdir failed: {e}"))
+            })?;
+        }
+
+        let tmp = dest.with_extension("tmp");
+        let mut file = fs::File::create(&tmp)
+            .await
+            .map_err(|e| DomainError::internal_error("BlobCache", format!("create tmp: {e}")))?;
+
+        use futures::StreamExt;
+        let mut stream = stream;
+        let mut total = 0u64;
+        while let Some(chunk) = stream.next().await {
+            let bytes = chunk.map_err(|e| {
+                DomainError::internal_error("BlobCache", format!("stream read: {e}"))
+            })?;
+            total += bytes.len() as u64;
+            file.write_all(&bytes)
+                .await
+                .map_err(|e| DomainError::internal_error("BlobCache", format!("write: {e}")))?;
+        }
+        file.flush()
+            .await
+            .map_err(|e| DomainError::internal_error("BlobCache", format!("flush: {e}")))?;
+        drop(file);
+
+        fs::rename(&tmp, &dest)
+            .await
+            .map_err(|e| DomainError::internal_error("BlobCache", format!("rename: {e}")))?;
+
+        let mut idx = self.index.lock().await;
+        if let Some(old) = idx.put(hash.to_string(), CacheEntry { size: total }) {
+            self.current_size.fetch_sub(old.size, Ordering::Relaxed);
+        }
+        self.current_size.fetch_add(total, Ordering::Relaxed);
+
+        while self.current_size.load(Ordering::Relaxed) > self.max_cache_bytes {
+            if let Some((evicted_hash, evicted_entry)) = idx.pop_lru() {
+                self.current_size
+                    .fetch_sub(evicted_entry.size, Ordering::Relaxed);
+                let evicted_path = self.cached_path(&evicted_hash);
+                let _ = fs::remove_file(&evicted_path).await;
+            } else {
+                break;
+            }
+        }
+
+        Ok(dest)
+    }
+}

src/infrastructure/services/dedup_service.rs

@@ -39,24 +39,22 @@ use sqlx::PgPool;
 use std::path::{Path, PathBuf};
 use std::pin::Pin;
 use std::sync::Arc;
-use tokio::fs::{self, File};
-use tokio::io::{AsyncReadExt, AsyncSeekExt};
-use tokio_util::io::ReaderStream;
+use tokio::fs;
 
+use crate::application::ports::blob_storage_ports::BlobStorageBackend;
 use crate::application::ports::dedup_ports::{
     BlobMetadataDto, DedupPort, DedupResultDto, DedupStatsDto,
 };
 use crate::domain::errors::{DomainError, ErrorKind};
 
-/// Chunk size for streaming file reads (256 KB)
-const STREAM_CHUNK_SIZE: usize = 256 * 1024;
-
 /// Content-Addressable Storage Service (PostgreSQL-backed)
+///
+/// Delegates all byte-level I/O to a [`BlobStorageBackend`] implementation
+/// (local filesystem, S3, etc.) while keeping BLAKE3 hashing, ref-counting
+/// and the PostgreSQL dedup index here.
 pub struct DedupService {
-    /// Root directory for blob storage on the filesystem
-    blob_root: PathBuf,
-    /// Root directory for temporary files during upload
-    temp_root: PathBuf,
+    /// Pluggable blob storage backend (local FS, S3, …).
+    backend: Arc<dyn BlobStorageBackend>,
     /// PostgreSQL connection pool (dedup index in `storage.blobs`) — primary,
     /// used by request-path operations (store_from_file, etc.).
     pool: Arc<PgPool>,
@@ -65,39 +63,19 @@ pub struct DedupService {
     maintenance_pool: Arc<PgPool>,
 }
 
-/// Compile-time lookup table for the 256 two-digit lowercase hex prefixes ("00"…"ff").
-/// Avoids a `format!("{:02x}", i)` allocation on every iteration of `initialize()`.
-static HEX_PREFIXES: [&str; 256] = [
-    "00", "01", "02", "03", "04", "05", "06", "07", "08", "09", "0a", "0b", "0c", "0d", "0e", "0f",
-    "10", "11", "12", "13", "14", "15", "16", "17", "18", "19", "1a", "1b", "1c", "1d", "1e", "1f",
-    "20", "21", "22", "23", "24", "25", "26", "27", "28", "29", "2a", "2b", "2c", "2d", "2e", "2f",
-    "30", "31", "32", "33", "34", "35", "36", "37", "38", "39", "3a", "3b", "3c", "3d", "3e", "3f",
-    "40", "41", "42", "43", "44", "45", "46", "47", "48", "49", "4a", "4b", "4c", "4d", "4e", "4f",
-    "50", "51", "52", "53", "54", "55", "56", "57", "58", "59", "5a", "5b", "5c", "5d", "5e", "5f",
-    "60", "61", "62", "63", "64", "65", "66", "67", "68", "69", "6a", "6b", "6c", "6d", "6e", "6f",
-    "70", "71", "72", "73", "74", "75", "76", "77", "78", "79", "7a", "7b", "7c", "7d", "7e", "7f",
-    "80", "81", "82", "83", "84", "85", "86", "87", "88", "89", "8a", "8b", "8c", "8d", "8e", "8f",
-    "90", "91", "92", "93", "94", "95", "96", "97", "98", "99", "9a", "9b", "9c", "9d", "9e", "9f",
-    "a0", "a1", "a2", "a3", "a4", "a5", "a6", "a7", "a8", "a9", "aa", "ab", "ac", "ad", "ae", "af",
-    "b0", "b1", "b2", "b3", "b4", "b5", "b6", "b7", "b8", "b9", "ba", "bb", "bc", "bd", "be", "bf",
-    "c0", "c1", "c2", "c3", "c4", "c5", "c6", "c7", "c8", "c9", "ca", "cb", "cc", "cd", "ce", "cf",
-    "d0", "d1", "d2", "d3", "d4", "d5", "d6", "d7", "d8", "d9", "da", "db", "dc", "dd", "de", "df",
-    "e0", "e1", "e2", "e3", "e4", "e5", "e6", "e7", "e8", "e9", "ea", "eb", "ec", "ed", "ee", "ef",
-    "f0", "f1", "f2", "f3", "f4", "f5", "f6", "f7", "f8", "f9", "fa", "fb", "fc", "fd", "fe", "ff",
-];
-
 impl DedupService {
     /// Create a new dedup service backed by PostgreSQL.
     ///
+    /// * `backend` — pluggable blob storage (local filesystem, S3, etc.).
     /// * `pool` — primary pool for request-path operations.
     /// * `maintenance_pool` — isolated pool for verify_integrity / garbage_collect.
-    pub fn new(storage_root: &Path, pool: Arc<PgPool>, maintenance_pool: Arc<PgPool>) -> Self {
-        let blob_root = storage_root.join(".blobs");
-        let temp_root = storage_root.join(".dedup_temp");
-
+    pub fn new(
+        backend: Arc<dyn BlobStorageBackend>,
+        pool: Arc<PgPool>,
+        maintenance_pool: Arc<PgPool>,
+    ) -> Self {
         Self {
-            blob_root,
-            temp_root,
+            backend,
             pool,
             maintenance_pool,
         }
@@ -106,6 +84,7 @@ impl DedupService {
     /// Creates a stub instance for testing — never hits PG or the filesystem.
     #[cfg(any(test, feature = "integration_tests"))]
     pub fn new_stub() -> Self {
+        use crate::infrastructure::services::local_blob_backend::LocalBlobBackend;
         let stub_pool = Arc::new(
             sqlx::pool::PoolOptions::<sqlx::Postgres>::new()
                 .max_connections(1)
@@ -113,29 +92,15 @@ impl DedupService {
                 .unwrap(),
         );
         Self {
-            blob_root: std::path::PathBuf::from("/tmp/oxicloud_stub_blobs"),
-            temp_root: std::path::PathBuf::from("/tmp/oxicloud_stub_temp"),
+            backend: Arc::new(LocalBlobBackend::new(Path::new("/tmp/oxicloud_stub_blobs"))),
             pool: stub_pool.clone(),
             maintenance_pool: stub_pool,
         }
     }
 
-    /// Initialize the service (create blob directories on the filesystem).
+    /// Initialize the service (delegate to backend + log stats from PG).
     pub async fn initialize(&self) -> Result<(), DomainError> {
-        // Create directories
-        fs::create_dir_all(&self.blob_root)
-            .await
-            .map_err(DomainError::from)?;
-        fs::create_dir_all(&self.temp_root)
-            .await
-            .map_err(DomainError::from)?;
-
-        // Create hash prefix directories (00-ff)
-        for prefix in &HEX_PREFIXES {
-            fs::create_dir_all(self.blob_root.join(prefix))
-                .await
-                .map_err(DomainError::from)?;
-        }
+        self.backend.initialize().await?;
 
         // Log existing blob stats from PG
         let count: i64 = sqlx::query_scalar("SELECT COUNT(*) FROM storage.blobs")
@@ -150,7 +115,8 @@ impl DedupService {
                 .unwrap_or(0);
 
         tracing::info!(
-            "Dedup service initialized (PostgreSQL-backed): {} blobs, {} bytes stored",
+            "Dedup service initialized (backend={}): {} blobs, {} bytes stored",
+            self.backend.backend_type(),
             count,
             total_bytes
         );
@@ -158,12 +124,18 @@ impl DedupService {
         Ok(())
     }
 
+    /// Return a reference to the underlying blob storage backend.
+    pub fn backend(&self) -> &Arc<dyn BlobStorageBackend> {
+        &self.backend
+    }
+
     // ── Path helpers ─────────────────────────────────────────────
 
-    /// Get the blob path for a given hash.
+    /// Get the local blob path for a given hash (if the backend supports it).
     pub fn blob_path(&self, hash: &str) -> PathBuf {
-        let prefix = &hash[0..2];
-        self.blob_root.join(prefix).join(format!("{}.blob", hash))
+        self.backend
+            .local_blob_path(hash)
+            .unwrap_or_else(|| PathBuf::from(format!("remote://{}", hash)))
     }
 
     // ── Hash helpers ─────────────────────────────────────────────
@@ -193,9 +165,9 @@ impl DedupService {
 
     /// Store content with deduplication (streaming from file).
     ///
-    /// **Write-first strategy**: the source file is moved/copied to the
-    /// blob store *before* touching PostgreSQL, so the PG connection is
-    /// never held during disk I/O.
+    /// **Write-first strategy**: the source file is moved/uploaded to the
+    /// blob backend *before* touching PostgreSQL, so the PG connection is
+    /// never held during I/O.
     ///
     /// If `pre_computed_hash` is `Some`, the file will NOT be re-read for
     /// BLAKE3 — saving one full sequential read (the biggest I/O win).
@@ -205,13 +177,6 @@ impl DedupService {
         content_type: Option<String>,
         pre_computed_hash: Option<String>,
     ) -> Result<DedupResultDto, DomainError> {
-        let file_size = fs::metadata(source_path)
-            .await
-            .map_err(|e| {
-                DomainError::internal_error("Dedup", format!("Failed to get file metadata: {}", e))
-            })?
-            .len();
-
         // Use pre-computed hash if available, otherwise calculate (streaming)
         let hash = match pre_computed_hash {
             Some(h) => h,
@@ -220,44 +185,11 @@ impl DedupService {
                 .map_err(DomainError::from)?,
         };
 
+        // ── Phase 1: Place blob in backend (NO PG connection held) ───
+        let file_size = self.backend.put_blob(&hash, source_path).await?;
+
         let blob_path = self.blob_path(&hash);
 
-        // ── Phase 1: Move/place blob on disk (NO PG connection held) ─
-        //
-        // If the blob file already exists on disk, the source is simply
-        // deleted — the file content is identical by definition.
-        if fs::try_exists(&blob_path).await.unwrap_or(false) {
-            // Blob already on disk — discard the source file
-            let _ = fs::remove_file(source_path).await;
-        } else {
-            // Parent directory (xx/) guaranteed to exist — created by initialize()
-
-            // rename is atomic on the same filesystem.  If source and blob
-            // dirs live on different filesystems (rare), this falls back to
-            // copy+delete which is slower but still correct.
-            if let Err(e) = fs::rename(source_path, &blob_path).await {
-                if e.raw_os_error() == Some(18) {
-                    // EXDEV: cross-device link — fall back to copy+delete
-                    fs::copy(source_path, &blob_path).await.map_err(|ce| {
-                        DomainError::internal_error(
-                            "Dedup",
-                            format!("Failed to copy file to blob store: {}", ce),
-                        )
-                    })?;
-                    let _ = fs::remove_file(source_path).await;
-                } else if fs::try_exists(&blob_path).await.unwrap_or(false) {
-                    // Another writer may have placed the blob concurrently
-                    let _ = fs::remove_file(source_path).await;
-                    tracing::debug!("Blob file placed by concurrent writer: {}", e);
-                } else {
-                    return Err(DomainError::internal_error(
-                        "Dedup",
-                        format!("Failed to move file to blob store: {}", e),
-                    ));
-                }
-            }
-        }
-
         // ── Phase 2: Single atomic upsert (~2-4 ms, no explicit TX) ─
         let ref_count: i32 = sqlx::query_scalar(
             "INSERT INTO storage.blobs (hash, size, ref_count, content_type)
@@ -415,10 +347,9 @@ impl DedupService {
                 DomainError::internal_error("Dedup", format!("Failed to commit: {}", e))
             })?;
 
-            // Delete blob file AFTER committing PG — the row is gone, so no
-            // concurrent store_from_file can resurrect a reference to this hash.
-            let blob_path = self.blob_path(hash);
-            if let Err(e) = fs::remove_file(&blob_path).await {
+            // Delete blob from backend AFTER committing PG — the row is gone,
+            // so no concurrent store_from_file can resurrect a reference.
+            if let Err(e) = self.backend.delete_blob(hash).await {
                 tracing::warn!("Failed to delete blob file {}: {}", hash, e);
             }
 
@@ -449,31 +380,16 @@ impl DedupService {
 
     // ── Read operations ──────────────────────────────────────────
 
-    /// Stream blob content in 64 KB chunks — constant memory (~64 KB per stream).
-    ///
-    /// A 1 GB file uses the same ~64 KB as a 1 KB file.
+    /// Stream blob content in chunks — constant memory usage.
     pub async fn read_blob_stream(
         &self,
         hash: &str,
     ) -> Result<Pin<Box<dyn Stream<Item = Result<Bytes, std::io::Error>> + Send>>, DomainError>
     {
-        let blob_path = self.blob_path(hash);
-        let file = File::open(&blob_path).await.map_err(|e| {
-            DomainError::new(
-                ErrorKind::NotFound,
-                "Blob",
-                format!("Failed to open blob {}: {}", hash, e),
-            )
-        })?;
-        Ok(Box::pin(ReaderStream::with_capacity(
-            file,
-            STREAM_CHUNK_SIZE,
-        )))
+        self.backend.get_blob_stream(hash).await
     }
 
     /// Stream a byte range of a blob — only reads the requested portion.
-    ///
-    /// Uses seek + take so a 1 MB range request on a 1 GB file only reads 1 MB.
     pub async fn read_blob_range_stream(
         &self,
         hash: &str,
@@ -481,49 +397,12 @@ impl DedupService {
         end: Option<u64>,
     ) -> Result<Pin<Box<dyn Stream<Item = Result<Bytes, std::io::Error>> + Send>>, DomainError>
     {
-        let blob_path = self.blob_path(hash);
-        let mut file = File::open(&blob_path).await.map_err(|e| {
-            DomainError::new(
-                ErrorKind::NotFound,
-                "Blob",
-                format!("Failed to open blob {}: {}", hash, e),
-            )
-        })?;
-
-        // Seek to the start position
-        file.seek(std::io::SeekFrom::Start(start))
-            .await
-            .map_err(|e| {
-                DomainError::internal_error("Blob", format!("Failed to seek in blob: {}", e))
-            })?;
-
-        // If an end is specified, limit the read with take()
-        if let Some(end_pos) = end {
-            let limit = end_pos.saturating_sub(start);
-            let limited = file.take(limit);
-            Ok(Box::pin(ReaderStream::with_capacity(
-                limited,
-                STREAM_CHUNK_SIZE,
-            )))
-        } else {
-            Ok(Box::pin(ReaderStream::with_capacity(
-                file,
-                STREAM_CHUNK_SIZE,
-            )))
-        }
+        self.backend.get_blob_range_stream(hash, start, end).await
     }
 
     /// Get the size of a blob without reading its content.
     pub async fn blob_size(&self, hash: &str) -> Result<u64, DomainError> {
-        let blob_path = self.blob_path(hash);
-        let meta = fs::metadata(&blob_path).await.map_err(|e| {
-            DomainError::new(
-                ErrorKind::NotFound,
-                "Blob",
-                format!("Failed to stat blob {}: {}", hash, e),
-            )
-        })?;
-        Ok(meta.len())
+        self.backend.blob_size(hash).await
     }
 
     // ── Statistics (computed from PG) ────────────────────────────
@@ -596,56 +475,46 @@ impl DedupService {
 
             // Flush when batch is full or we've exhausted the cursor
             if batch.len() >= VERIFY_CONCURRENCY || (is_done && !batch.is_empty()) {
-                let blob_root = self.blob_root.clone();
+                let backend = self.backend.clone();
                 let current_batch =
                     std::mem::replace(&mut batch, Vec::with_capacity(VERIFY_CONCURRENCY));
 
                 let issues: Vec<String> = stream::iter(current_batch)
                     .map(move |(hash, expected_size)| {
-                        let blob_root = blob_root.clone();
+                        let backend = backend.clone();
                         async move {
-                            let prefix = &hash[0..2];
-                            let blob_path = blob_root.join(prefix).join(format!("{}.blob", hash));
-
                             let mut issues = Vec::new();
 
-                            // Single async metadata() replaces the previous
-                            // blocking .exists() + separate metadata() — one
-                            // stat() syscall instead of two, and non-blocking.
-                            let file_meta = match fs::metadata(&blob_path).await {
-                                Ok(m) => m,
-                                Err(e) if e.kind() == std::io::ErrorKind::NotFound => {
-                                    issues.push(format!("{}: file missing on disk", hash));
-                                    return issues;
+                            // Check existence + size via backend
+                            match backend.blob_size(&hash).await {
+                                Ok(actual_size) => {
+                                    if actual_size != expected_size as u64 {
+                                        issues.push(format!(
+                                            "{}: size mismatch (expected: {}, actual: {})",
+                                            hash, expected_size, actual_size,
+                                        ));
+                                    }
                                 }
-                                Err(e) => {
-                                    issues.push(format!("{}: metadata error ({})", hash, e));
+                                Err(_) => {
+                                    issues.push(format!("{}: blob missing in backend", hash));
                                     return issues;
                                 }
                             };
 
-                            // Check size
-                            if file_meta.len() != expected_size as u64 {
-                                issues.push(format!(
-                                    "{}: size mismatch (expected: {}, actual: {})",
-                                    hash,
-                                    expected_size,
-                                    file_meta.len(),
-                                ));
-                            }
-
-                            // Verify hash
-                            match Self::hash_file(&blob_path).await {
-                                Ok(actual_hash) => {
-                                    if actual_hash != hash {
-                                        issues.push(format!(
-                                            "{}: hash mismatch (actual: {})",
-                                            hash, actual_hash,
-                                        ));
+                            // Verify hash — only possible for local backends
+                            if let Some(blob_path) = backend.local_blob_path(&hash) {
+                                match Self::hash_file(&blob_path).await {
+                                    Ok(actual_hash) => {
+                                        if actual_hash != hash {
+                                            issues.push(format!(
+                                                "{}: hash mismatch (actual: {})",
+                                                hash, actual_hash,
+                                            ));
+                                        }
+                                    }
+                                    Err(e) => {
+                                        issues.push(format!("{}: read error ({})", hash, e));
                                     }
-                                }
-                                Err(e) => {
-                                    issues.push(format!("{}: read error ({})", hash, e));
                                 }
                             }
 
@@ -717,20 +586,20 @@ impl DedupService {
             // Also clean up any thumbnail files for these blob hashes
             // (thumbnails are keyed by blob_hash and live under
             // storage_root/.thumbnails/{icon,preview,large}/{hash}.jpg).
-            let thumbnails_root = self
-                .blob_root
-                .parent()
-                .unwrap_or(&self.blob_root)
-                .join(".thumbnails");
+
             for (hash, size) in &batch {
-                let blob_path = self.blob_path(hash);
-                if let Err(e) = fs::remove_file(&blob_path).await {
+                if let Err(e) = self.backend.delete_blob(hash).await {
                     tracing::warn!("Failed to delete orphan blob file {hash}: {e}");
                 }
-                // Remove associated thumbnail files (best-effort)
-                for dir in &["icon", "preview", "large"] {
-                    let thumb = thumbnails_root.join(dir).join(format!("{hash}.jpg"));
-                    let _ = fs::remove_file(&thumb).await;
+                // Remove associated thumbnail files (best-effort, always local)
+                if let Some(blob_path) = self.backend.local_blob_path(hash)
+                    && let Some(storage_root) = blob_path.ancestors().nth(3)
+                {
+                    let thumbnails_root = storage_root.join(".thumbnails");
+                    for dir in &["icon", "preview", "large"] {
+                        let thumb = thumbnails_root.join(dir).join(format!("{hash}.jpg"));
+                        let _ = fs::remove_file(&thumb).await;
+                    }
                 }
                 total_bytes += *size as u64;
             }

src/infrastructure/services/encrypted_blob_backend.rs

@@ -0,0 +1,298 @@
+//! `EncryptedBlobBackend` — AES-256-GCM encryption decorator for blob storage.
+//!
+//! Transparently encrypts blobs before they reach the inner backend and
+//! decrypts them on read.  Each blob gets a random 96-bit nonce which is
+//! prepended to the ciphertext.  The GCM authentication tag (16 bytes) is
+//! appended by the cipher.
+//!
+//! **IMPORTANT**: BLAKE3 hashing is performed on the *plaintext* by
+//! `DedupService` before this layer sees the blob, so content-addressable
+//! dedup still works correctly.
+//!
+//! Layout on disk/S3: `[12-byte nonce][ciphertext + 16-byte GCM tag]`
+
+use std::path::{Path, PathBuf};
+use std::pin::Pin;
+
+use aes_gcm::aead::{Aead, KeyInit, OsRng};
+use aes_gcm::{AeadCore, Aes256Gcm, Nonce};
+use bytes::Bytes;
+use std::sync::Arc;
+use tokio::fs;
+use tokio::io::AsyncWriteExt;
+
+use crate::application::ports::blob_storage_ports::{
+    BlobStorageBackend, BlobStream, StorageHealthStatus,
+};
+use crate::domain::errors::DomainError;
+
+/// Nonce size for AES-256-GCM (96 bits = 12 bytes).
+const NONCE_SIZE: usize = 12;
+
+/// `BlobStorageBackend` decorator that encrypts blobs at rest.
+pub struct EncryptedBlobBackend {
+    inner: Arc<dyn BlobStorageBackend>,
+    cipher: Aes256Gcm,
+}
+
+impl EncryptedBlobBackend {
+    /// Create a new encryption layer wrapping `inner`.
+    ///
+    /// `key` must be exactly 32 bytes (AES-256).
+    pub fn new(inner: Arc<dyn BlobStorageBackend>, key: &[u8; 32]) -> Self {
+        let cipher = Aes256Gcm::new_from_slice(key).expect("AES-256 key must be 32 bytes");
+        Self { inner, cipher }
+    }
+
+    /// Generate a random 32-byte key suitable for AES-256.
+    pub fn generate_key() -> [u8; 32] {
+        use aes_gcm::aead::rand_core::RngCore;
+        let mut key = [0u8; 32];
+        OsRng.fill_bytes(&mut key);
+        key
+    }
+}
+
+impl BlobStorageBackend for EncryptedBlobBackend {
+    fn initialize(
+        &self,
+    ) -> Pin<Box<dyn std::future::Future<Output = Result<(), DomainError>> + Send + '_>> {
+        self.inner.initialize()
+    }
+
+    fn put_blob(
+        &self,
+        hash: &str,
+        source_path: &Path,
+    ) -> Pin<Box<dyn std::future::Future<Output = Result<u64, DomainError>> + Send + '_>> {
+        let inner = self.inner.clone();
+        let hash = hash.to_string();
+        let source = source_path.to_path_buf();
+        // Clone cipher key material (Aes256Gcm is not Send-safe to move across await)
+        let cipher = self.cipher.clone();
+        Box::pin(async move {
+            // Read plaintext from source
+            let plaintext = fs::read(&source).await.map_err(|e| {
+                DomainError::internal_error("Encryption", format!("read source: {e}"))
+            })?;
+
+            // Encrypt: nonce || ciphertext (includes GCM tag)
+            let nonce = Aes256Gcm::generate_nonce(&mut OsRng);
+            let ciphertext = cipher.encrypt(&nonce, plaintext.as_ref()).map_err(|e| {
+                DomainError::internal_error("Encryption", format!("encrypt failed: {e}"))
+            })?;
+
+            // Write encrypted blob to a temp file
+            let tmp = source.with_extension("enc.tmp");
+            let mut file = fs::File::create(&tmp).await.map_err(|e| {
+                DomainError::internal_error("Encryption", format!("create tmp: {e}"))
+            })?;
+            file.write_all(nonce.as_slice()).await.map_err(|e| {
+                DomainError::internal_error("Encryption", format!("write nonce: {e}"))
+            })?;
+            file.write_all(&ciphertext).await.map_err(|e| {
+                DomainError::internal_error("Encryption", format!("write ciphertext: {e}"))
+            })?;
+            file.flush()
+                .await
+                .map_err(|e| DomainError::internal_error("Encryption", format!("flush: {e}")))?;
+            drop(file);
+
+            let result = inner.put_blob(&hash, &tmp).await;
+            let _ = fs::remove_file(&tmp).await;
+            result
+        })
+    }
+
+    fn get_blob_stream(
+        &self,
+        hash: &str,
+    ) -> Pin<Box<dyn std::future::Future<Output = Result<BlobStream, DomainError>> + Send + '_>>
+    {
+        let inner = self.inner.clone();
+        let hash = hash.to_string();
+        let cipher = self.cipher.clone();
+        Box::pin(async move {
+            // Read entire encrypted blob (nonce + ciphertext) into memory for decryption
+            let enc_stream = inner.get_blob_stream(&hash).await?;
+            let encrypted = collect_stream(enc_stream).await?;
+
+            if encrypted.len() < NONCE_SIZE {
+                return Err(DomainError::internal_error(
+                    "Encryption",
+                    "encrypted blob too short (missing nonce)",
+                ));
+            }
+
+            let (nonce_bytes, ciphertext) = encrypted.split_at(NONCE_SIZE);
+            let nonce = Nonce::from_slice(nonce_bytes);
+            let plaintext = cipher.decrypt(nonce, ciphertext).map_err(|e| {
+                DomainError::internal_error("Encryption", format!("decrypt failed: {e}"))
+            })?;
+
+            let stream: BlobStream =
+                Box::pin(futures::stream::once(
+                    async move { Ok(Bytes::from(plaintext)) },
+                ));
+            Ok(stream)
+        })
+    }
+
+    fn get_blob_range_stream(
+        &self,
+        hash: &str,
+        start: u64,
+        end: Option<u64>,
+    ) -> Pin<Box<dyn std::future::Future<Output = Result<BlobStream, DomainError>> + Send + '_>>
+    {
+        let inner = self.inner.clone();
+        let hash = hash.to_string();
+        let cipher = self.cipher.clone();
+        Box::pin(async move {
+            // Must decrypt the full blob then slice the plaintext range
+            let enc_stream = inner.get_blob_stream(&hash).await?;
+            let encrypted = collect_stream(enc_stream).await?;
+
+            if encrypted.len() < NONCE_SIZE {
+                return Err(DomainError::internal_error(
+                    "Encryption",
+                    "encrypted blob too short",
+                ));
+            }
+
+            let (nonce_bytes, ciphertext) = encrypted.split_at(NONCE_SIZE);
+            let nonce = Nonce::from_slice(nonce_bytes);
+            let plaintext = cipher.decrypt(nonce, ciphertext).map_err(|e| {
+                DomainError::internal_error("Encryption", format!("decrypt failed: {e}"))
+            })?;
+
+            let start = start as usize;
+            let end = end.map(|e| (e as usize) + 1).unwrap_or(plaintext.len());
+            let end = end.min(plaintext.len());
+            let start = start.min(end);
+
+            let slice = Bytes::from(plaintext[start..end].to_vec());
+            let stream: BlobStream = Box::pin(futures::stream::once(async move { Ok(slice) }));
+            Ok(stream)
+        })
+    }
+
+    fn delete_blob(
+        &self,
+        hash: &str,
+    ) -> Pin<Box<dyn std::future::Future<Output = Result<(), DomainError>> + Send + '_>> {
+        self.inner.delete_blob(hash)
+    }
+
+    fn blob_exists(
+        &self,
+        hash: &str,
+    ) -> Pin<Box<dyn std::future::Future<Output = Result<bool, DomainError>> + Send + '_>> {
+        self.inner.blob_exists(hash)
+    }
+
+    fn blob_size(
+        &self,
+        hash: &str,
+    ) -> Pin<Box<dyn std::future::Future<Output = Result<u64, DomainError>> + Send + '_>> {
+        // The stored size includes nonce + GCM tag overhead.
+        // Return the *plaintext* size by subtracting overhead.
+        let inner = self.inner.clone();
+        let hash = hash.to_string();
+        Box::pin(async move {
+            let encrypted_size = inner.blob_size(&hash).await?;
+            // overhead = 12 (nonce) + 16 (GCM tag) = 28 bytes
+            Ok(encrypted_size.saturating_sub(28))
+        })
+    }
+
+    fn health_check(
+        &self,
+    ) -> Pin<
+        Box<dyn std::future::Future<Output = Result<StorageHealthStatus, DomainError>> + Send + '_>,
+    > {
+        let inner = self.inner.clone();
+        Box::pin(async move {
+            let mut status = inner.health_check().await?;
+            status.backend_type = format!("encrypted({})", status.backend_type);
+            status.message = format!("{} | Encryption: AES-256-GCM", status.message);
+            Ok(status)
+        })
+    }
+
+    fn backend_type(&self) -> &'static str {
+        "encrypted"
+    }
+
+    fn local_blob_path(&self, _hash: &str) -> Option<PathBuf> {
+        // Encrypted blobs cannot be served directly from disk
+        None
+    }
+}
+
+/// Collect a byte stream into a single `Vec<u8>`.
+async fn collect_stream(stream: BlobStream) -> Result<Vec<u8>, DomainError> {
+    use futures::StreamExt;
+    let mut stream = stream;
+    let mut buf = Vec::new();
+    while let Some(chunk) = stream.next().await {
+        let bytes = chunk
+            .map_err(|e| DomainError::internal_error("Encryption", format!("stream read: {e}")))?;
+        buf.extend_from_slice(&bytes);
+    }
+    Ok(buf)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::infrastructure::services::local_blob_backend::LocalBlobBackend;
+    use tempfile::TempDir;
+    use tokio::io::AsyncWriteExt;
+
+    #[tokio::test]
+    async fn test_encrypt_decrypt_roundtrip() {
+        let tmp = TempDir::new().unwrap();
+        let blob_dir = tmp.path().join("blobs");
+        let local = Arc::new(LocalBlobBackend::new(&blob_dir));
+        local.initialize().await.unwrap();
+
+        let key = EncryptedBlobBackend::generate_key();
+        let encrypted = EncryptedBlobBackend::new(local, &key);
+
+        // Write a test blob
+        let data = b"Hello, encrypted world!";
+        let source = tmp.path().join("test.tmp");
+        let mut f = fs::File::create(&source).await.unwrap();
+        f.write_all(data).await.unwrap();
+        f.flush().await.unwrap();
+        drop(f);
+
+        let hash = "abcdef1234567890abcdef1234567890abcdef1234567890abcdef1234567890";
+        encrypted.put_blob(hash, &source).await.unwrap();
+
+        // Read back via stream
+        let stream = encrypted.get_blob_stream(hash).await.unwrap();
+        let decrypted = collect_stream(stream).await.unwrap();
+        assert_eq!(decrypted, data);
+
+        // Read range
+        let range_stream = encrypted
+            .get_blob_range_stream(hash, 7, Some(15))
+            .await
+            .unwrap();
+        let range_data = collect_stream(range_stream).await.unwrap();
+        assert_eq!(range_data, b"encrypted");
+
+        // Size should reflect plaintext
+        let size = encrypted.blob_size(hash).await.unwrap();
+        assert_eq!(size, data.len() as u64);
+
+        // Exists
+        assert!(encrypted.blob_exists(hash).await.unwrap());
+
+        // Delete
+        encrypted.delete_blob(hash).await.unwrap();
+        assert!(!encrypted.blob_exists(hash).await.unwrap());
+    }
+}

src/infrastructure/services/local_blob_backend.rs

@@ -0,0 +1,277 @@
+//! Local Filesystem Blob Backend — stores blobs under `.blobs/{prefix}/{hash}.blob`.
+//!
+//! This is the default backend and a direct extraction of the filesystem I/O
+//! that previously lived inside `DedupService`.
+
+use std::path::{Path, PathBuf};
+use std::pin::Pin;
+use tokio::fs::{self, File};
+use tokio::io::AsyncSeekExt;
+use tokio_util::io::ReaderStream;
+
+use crate::application::ports::blob_storage_ports::{
+    BlobStorageBackend, BlobStream, StorageHealthStatus,
+};
+use crate::domain::errors::{DomainError, ErrorKind};
+
+/// Chunk size for streaming file reads (256 KB).
+const STREAM_CHUNK_SIZE: usize = 256 * 1024;
+
+/// Compile-time lookup table for the 256 two-digit lowercase hex prefixes ("00"…"ff").
+static HEX_PREFIXES: [&str; 256] = [
+    "00", "01", "02", "03", "04", "05", "06", "07", "08", "09", "0a", "0b", "0c", "0d", "0e", "0f",
+    "10", "11", "12", "13", "14", "15", "16", "17", "18", "19", "1a", "1b", "1c", "1d", "1e", "1f",
+    "20", "21", "22", "23", "24", "25", "26", "27", "28", "29", "2a", "2b", "2c", "2d", "2e", "2f",
+    "30", "31", "32", "33", "34", "35", "36", "37", "38", "39", "3a", "3b", "3c", "3d", "3e", "3f",
+    "40", "41", "42", "43", "44", "45", "46", "47", "48", "49", "4a", "4b", "4c", "4d", "4e", "4f",
+    "50", "51", "52", "53", "54", "55", "56", "57", "58", "59", "5a", "5b", "5c", "5d", "5e", "5f",
+    "60", "61", "62", "63", "64", "65", "66", "67", "68", "69", "6a", "6b", "6c", "6d", "6e", "6f",
+    "70", "71", "72", "73", "74", "75", "76", "77", "78", "79", "7a", "7b", "7c", "7d", "7e", "7f",
+    "80", "81", "82", "83", "84", "85", "86", "87", "88", "89", "8a", "8b", "8c", "8d", "8e", "8f",
+    "90", "91", "92", "93", "94", "95", "96", "97", "98", "99", "9a", "9b", "9c", "9d", "9e", "9f",
+    "a0", "a1", "a2", "a3", "a4", "a5", "a6", "a7", "a8", "a9", "aa", "ab", "ac", "ad", "ae", "af",
+    "b0", "b1", "b2", "b3", "b4", "b5", "b6", "b7", "b8", "b9", "ba", "bb", "bc", "bd", "be", "bf",
+    "c0", "c1", "c2", "c3", "c4", "c5", "c6", "c7", "c8", "c9", "ca", "cb", "cc", "cd", "ce", "cf",
+    "d0", "d1", "d2", "d3", "d4", "d5", "d6", "d7", "d8", "d9", "da", "db", "dc", "dd", "de", "df",
+    "e0", "e1", "e2", "e3", "e4", "e5", "e6", "e7", "e8", "e9", "ea", "eb", "ec", "ed", "ee", "ef",
+    "f0", "f1", "f2", "f3", "f4", "f5", "f6", "f7", "f8", "f9", "fa", "fb", "fc", "fd", "fe", "ff",
+];
+
+/// Local filesystem blob backend.
+///
+/// Blobs are stored under `blob_root/{2-char-prefix}/{hash}.blob`.
+/// Temporary upload staging uses `temp_root/`.
+pub struct LocalBlobBackend {
+    blob_root: PathBuf,
+    temp_root: PathBuf,
+}
+
+impl LocalBlobBackend {
+    /// Create a new local backend rooted at `storage_root`.
+    ///
+    /// Blob files go under `{storage_root}/.blobs/`, temp files under
+    /// `{storage_root}/.dedup_temp/`.
+    pub fn new(storage_root: &Path) -> Self {
+        Self {
+            blob_root: storage_root.join(".blobs"),
+            temp_root: storage_root.join(".dedup_temp"),
+        }
+    }
+
+    /// Compute the filesystem path for a blob hash.
+    pub fn blob_path(&self, hash: &str) -> PathBuf {
+        let prefix = &hash[0..2];
+        self.blob_root.join(prefix).join(format!("{}.blob", hash))
+    }
+
+    /// Return a reference to the blob root directory.
+    pub fn blob_root(&self) -> &Path {
+        &self.blob_root
+    }
+}
+
+impl BlobStorageBackend for LocalBlobBackend {
+    fn initialize(
+        &self,
+    ) -> Pin<Box<dyn std::future::Future<Output = Result<(), DomainError>> + Send + '_>> {
+        Box::pin(async move {
+            fs::create_dir_all(&self.blob_root)
+                .await
+                .map_err(DomainError::from)?;
+            fs::create_dir_all(&self.temp_root)
+                .await
+                .map_err(DomainError::from)?;
+
+            // Create the 256 hash-prefix directories (00-ff)
+            for prefix in &HEX_PREFIXES {
+                fs::create_dir_all(self.blob_root.join(prefix))
+                    .await
+                    .map_err(DomainError::from)?;
+            }
+            Ok(())
+        })
+    }
+
+    fn put_blob(
+        &self,
+        hash: &str,
+        source_path: &Path,
+    ) -> Pin<Box<dyn std::future::Future<Output = Result<u64, DomainError>> + Send + '_>> {
+        let hash = hash.to_owned();
+        let source_path = source_path.to_owned();
+        Box::pin(async move {
+            let blob_path = self.blob_path(&hash);
+
+            let file_size = fs::metadata(&source_path)
+                .await
+                .map_err(|e| {
+                    DomainError::internal_error(
+                        "Blob",
+                        format!("Failed to stat source file: {}", e),
+                    )
+                })?
+                .len();
+
+            // Idempotent: if blob already exists, just remove the source
+            if fs::try_exists(&blob_path).await.unwrap_or(false) {
+                let _ = fs::remove_file(&source_path).await;
+                return Ok(file_size);
+            }
+
+            // Atomic rename (same filesystem).  Falls back to copy+delete for
+            // cross-device moves (EXDEV errno 18).
+            if let Err(e) = fs::rename(&source_path, &blob_path).await {
+                if e.raw_os_error() == Some(18) {
+                    // EXDEV — cross-device link
+                    fs::copy(&source_path, &blob_path).await.map_err(|ce| {
+                        DomainError::internal_error(
+                            "Blob",
+                            format!("Failed to copy file to blob store: {}", ce),
+                        )
+                    })?;
+                    let _ = fs::remove_file(&source_path).await;
+                } else if fs::try_exists(&blob_path).await.unwrap_or(false) {
+                    // Concurrent writer placed the blob — discard our copy
+                    let _ = fs::remove_file(&source_path).await;
+                    tracing::debug!("Blob placed by concurrent writer: {}", e);
+                } else {
+                    return Err(DomainError::internal_error(
+                        "Blob",
+                        format!("Failed to move file to blob store: {}", e),
+                    ));
+                }
+            }
+
+            Ok(file_size)
+        })
+    }
+
+    fn get_blob_stream(
+        &self,
+        hash: &str,
+    ) -> Pin<Box<dyn std::future::Future<Output = Result<BlobStream, DomainError>> + Send + '_>>
+    {
+        let hash = hash.to_owned();
+        Box::pin(async move {
+            let blob_path = self.blob_path(&hash);
+            let file = File::open(&blob_path).await.map_err(|e| {
+                DomainError::new(
+                    ErrorKind::NotFound,
+                    "Blob",
+                    format!("Failed to open blob {}: {}", hash, e),
+                )
+            })?;
+            Ok(Box::pin(ReaderStream::with_capacity(file, STREAM_CHUNK_SIZE)) as BlobStream)
+        })
+    }
+
+    fn get_blob_range_stream(
+        &self,
+        hash: &str,
+        start: u64,
+        end: Option<u64>,
+    ) -> Pin<Box<dyn std::future::Future<Output = Result<BlobStream, DomainError>> + Send + '_>>
+    {
+        let hash = hash.to_owned();
+        Box::pin(async move {
+            let blob_path = self.blob_path(&hash);
+            let mut file = File::open(&blob_path).await.map_err(|e| {
+                DomainError::new(
+                    ErrorKind::NotFound,
+                    "Blob",
+                    format!("Failed to open blob {}: {}", hash, e),
+                )
+            })?;
+
+            file.seek(std::io::SeekFrom::Start(start))
+                .await
+                .map_err(|e| {
+                    DomainError::internal_error("Blob", format!("Failed to seek in blob: {}", e))
+                })?;
+
+            if let Some(end_pos) = end {
+                use tokio::io::AsyncReadExt;
+                let limit = end_pos.saturating_sub(start);
+                let limited = file.take(limit);
+                Ok(Box::pin(ReaderStream::with_capacity(limited, STREAM_CHUNK_SIZE)) as BlobStream)
+            } else {
+                Ok(Box::pin(ReaderStream::with_capacity(file, STREAM_CHUNK_SIZE)) as BlobStream)
+            }
+        })
+    }
+
+    fn delete_blob(
+        &self,
+        hash: &str,
+    ) -> Pin<Box<dyn std::future::Future<Output = Result<(), DomainError>> + Send + '_>> {
+        let hash = hash.to_owned();
+        Box::pin(async move {
+            let blob_path = self.blob_path(&hash);
+            match fs::remove_file(&blob_path).await {
+                Ok(()) => Ok(()),
+                Err(e) if e.kind() == std::io::ErrorKind::NotFound => Ok(()), // idempotent
+                Err(e) => Err(DomainError::internal_error(
+                    "Blob",
+                    format!("Failed to delete blob {}: {}", hash, e),
+                )),
+            }
+        })
+    }
+
+    fn blob_exists(
+        &self,
+        hash: &str,
+    ) -> Pin<Box<dyn std::future::Future<Output = Result<bool, DomainError>> + Send + '_>> {
+        let hash = hash.to_owned();
+        Box::pin(async move {
+            let blob_path = self.blob_path(&hash);
+            Ok(fs::try_exists(&blob_path).await.unwrap_or(false))
+        })
+    }
+
+    fn blob_size(
+        &self,
+        hash: &str,
+    ) -> Pin<Box<dyn std::future::Future<Output = Result<u64, DomainError>> + Send + '_>> {
+        let hash = hash.to_owned();
+        Box::pin(async move {
+            let blob_path = self.blob_path(&hash);
+            let meta = fs::metadata(&blob_path).await.map_err(|e| {
+                DomainError::new(
+                    ErrorKind::NotFound,
+                    "Blob",
+                    format!("Failed to stat blob {}: {}", hash, e),
+                )
+            })?;
+            Ok(meta.len())
+        })
+    }
+
+    fn health_check(
+        &self,
+    ) -> Pin<
+        Box<dyn std::future::Future<Output = Result<StorageHealthStatus, DomainError>> + Send + '_>,
+    > {
+        Box::pin(async move {
+            let writable = fs::metadata(&self.blob_root).await.is_ok();
+            Ok(StorageHealthStatus {
+                connected: writable,
+                backend_type: "local".to_string(),
+                message: if writable {
+                    "Local filesystem is accessible".to_string()
+                } else {
+                    "Blob root directory is not accessible".to_string()
+                },
+                available_bytes: None,
+            })
+        })
+    }
+
+    fn backend_type(&self) -> &'static str {
+        "local"
+    }
+
+    fn local_blob_path(&self, hash: &str) -> Option<PathBuf> {
+        Some(self.blob_path(hash))
+    }
+}

src/infrastructure/services/migration_blob_backend.rs

@@ -0,0 +1,204 @@
+//! `MigrationBlobBackend` — decorator that enables zero-downtime migration
+//! between blob storage backends.
+//!
+//! During a migration the decorator writes to the **target** backend and reads
+//! from **target-first-then-source** (dual-read).  A background job
+//! (see `migration_job.rs`) copies remaining blobs in the background.
+
+use std::future::Future;
+use std::path::{Path, PathBuf};
+use std::pin::Pin;
+use std::sync::Arc;
+
+use chrono::{DateTime, Utc};
+use serde::Serialize;
+use tokio::sync::RwLock;
+
+use crate::application::ports::blob_storage_ports::{
+    BlobStorageBackend, BlobStream, StorageHealthStatus,
+};
+use crate::common::errors::DomainError;
+
+// ── Migration state ────────────────────────────────────────────────
+
+/// Progress of an ongoing (or completed) backend migration.
+#[derive(Debug, Clone, Serialize)]
+pub struct MigrationState {
+    pub status: MigrationStatus,
+    pub total_blobs: u64,
+    pub migrated_blobs: u64,
+    pub migrated_bytes: u64,
+    pub failed_blobs: Vec<String>,
+    pub started_at: Option<DateTime<Utc>>,
+    pub completed_at: Option<DateTime<Utc>>,
+}
+
+impl Default for MigrationState {
+    fn default() -> Self {
+        Self {
+            status: MigrationStatus::Idle,
+            total_blobs: 0,
+            migrated_blobs: 0,
+            migrated_bytes: 0,
+            failed_blobs: Vec::new(),
+            started_at: None,
+            completed_at: None,
+        }
+    }
+}
+
+/// Status of the migration job.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize)]
+#[serde(rename_all = "snake_case")]
+pub enum MigrationStatus {
+    Idle,
+    Running,
+    Paused,
+    Completed,
+    Failed,
+}
+
+// ── MigrationBlobBackend ───────────────────────────────────────────
+
+/// A `BlobStorageBackend` decorator that proxies requests to a *source*
+/// (old) and *target* (new) backend, enabling live migration.
+pub struct MigrationBlobBackend {
+    source: Arc<dyn BlobStorageBackend>,
+    target: Arc<dyn BlobStorageBackend>,
+    state: Arc<RwLock<MigrationState>>,
+}
+
+impl MigrationBlobBackend {
+    pub fn new(
+        source: Arc<dyn BlobStorageBackend>,
+        target: Arc<dyn BlobStorageBackend>,
+        state: Arc<RwLock<MigrationState>>,
+    ) -> Self {
+        Self {
+            source,
+            target,
+            state,
+        }
+    }
+
+    pub fn state(&self) -> &Arc<RwLock<MigrationState>> {
+        &self.state
+    }
+
+    pub fn source(&self) -> &Arc<dyn BlobStorageBackend> {
+        &self.source
+    }
+
+    pub fn target(&self) -> &Arc<dyn BlobStorageBackend> {
+        &self.target
+    }
+}
+
+/// Boxed future alias (same as in the trait module).
+type BoxFut<'a, T> = Pin<Box<dyn Future<Output = T> + Send + 'a>>;
+
+impl BlobStorageBackend for MigrationBlobBackend {
+    fn initialize(&self) -> BoxFut<'_, Result<(), DomainError>> {
+        Box::pin(async move {
+            self.target.initialize().await?;
+            // Source is already initialised; call anyway for idempotency.
+            self.source.initialize().await?;
+            Ok(())
+        })
+    }
+
+    /// Writes go to **target** only.
+    fn put_blob(&self, hash: &str, source_path: &Path) -> BoxFut<'_, Result<u64, DomainError>> {
+        let hash = hash.to_string();
+        let path = source_path.to_path_buf();
+        Box::pin(async move { self.target.put_blob(&hash, &path).await })
+    }
+
+    /// Read from target first; fall back to source.
+    fn get_blob_stream(&self, hash: &str) -> BoxFut<'_, Result<BlobStream, DomainError>> {
+        let hash = hash.to_string();
+        Box::pin(async move {
+            match self.target.get_blob_stream(&hash).await {
+                Ok(stream) => Ok(stream),
+                Err(_) => self.source.get_blob_stream(&hash).await,
+            }
+        })
+    }
+
+    fn get_blob_range_stream(
+        &self,
+        hash: &str,
+        start: u64,
+        end: Option<u64>,
+    ) -> BoxFut<'_, Result<BlobStream, DomainError>> {
+        let hash = hash.to_string();
+        Box::pin(async move {
+            match self.target.get_blob_range_stream(&hash, start, end).await {
+                Ok(stream) => Ok(stream),
+                Err(_) => self.source.get_blob_range_stream(&hash, start, end).await,
+            }
+        })
+    }
+
+    /// Delete from **both** backends (best-effort on source).
+    fn delete_blob(&self, hash: &str) -> BoxFut<'_, Result<(), DomainError>> {
+        let hash = hash.to_string();
+        Box::pin(async move {
+            self.target.delete_blob(&hash).await?;
+            // Best-effort on source — ignore errors (blob may already be gone).
+            let _ = self.source.delete_blob(&hash).await;
+            Ok(())
+        })
+    }
+
+    /// Exists in either backend.
+    fn blob_exists(&self, hash: &str) -> BoxFut<'_, Result<bool, DomainError>> {
+        let hash = hash.to_string();
+        Box::pin(async move {
+            if self.target.blob_exists(&hash).await? {
+                return Ok(true);
+            }
+            self.source.blob_exists(&hash).await
+        })
+    }
+
+    fn blob_size(&self, hash: &str) -> BoxFut<'_, Result<u64, DomainError>> {
+        let hash = hash.to_string();
+        Box::pin(async move {
+            match self.target.blob_size(&hash).await {
+                Ok(sz) => Ok(sz),
+                Err(_) => self.source.blob_size(&hash).await,
+            }
+        })
+    }
+
+    fn health_check(&self) -> BoxFut<'_, Result<StorageHealthStatus, DomainError>> {
+        Box::pin(async move {
+            let target_health = self.target.health_check().await?;
+            let source_health = self.source.health_check().await?;
+            Ok(StorageHealthStatus {
+                connected: target_health.connected && source_health.connected,
+                backend_type: format!(
+                    "migration({} → {})",
+                    source_health.backend_type, target_health.backend_type
+                ),
+                message: format!(
+                    "Source: {} | Target: {}",
+                    source_health.message, target_health.message
+                ),
+                available_bytes: target_health.available_bytes,
+            })
+        })
+    }
+
+    fn backend_type(&self) -> &'static str {
+        "migration"
+    }
+
+    fn local_blob_path(&self, hash: &str) -> Option<PathBuf> {
+        // Prefer target, fall back to source.
+        self.target
+            .local_blob_path(hash)
+            .or_else(|| self.source.local_blob_path(hash))
+    }
+}

src/infrastructure/services/migration_job.rs

@@ -0,0 +1,240 @@
+//! Background migration job — copies blobs from a source backend to a target
+//! backend with configurable concurrency and progress tracking.
+
+use std::sync::Arc;
+
+use futures::StreamExt;
+use serde::Serialize;
+use sqlx::PgPool;
+use tokio::sync::RwLock;
+
+use crate::application::ports::blob_storage_ports::BlobStorageBackend;
+use crate::common::errors::DomainError;
+use crate::infrastructure::services::migration_blob_backend::{MigrationState, MigrationStatus};
+
+/// Run the migration: stream all blob hashes from `storage.blobs` and copy
+/// each one from `source` to `target`.
+///
+/// * The job respects `Paused` / `Failed` status in `state` — it will stop
+///   streaming when the status is no longer `Running`.
+/// * Errors on individual blobs are logged and collected in `failed_blobs`
+///   but do **not** abort the full run.
+/// * `concurrency` controls `buffer_unordered` parallelism (default: 4).
+pub async fn run_migration(
+    source: Arc<dyn BlobStorageBackend>,
+    target: Arc<dyn BlobStorageBackend>,
+    pool: Arc<PgPool>,
+    state: Arc<RwLock<MigrationState>>,
+    concurrency: usize,
+) -> Result<(), DomainError> {
+    // Count total blobs for progress tracking.
+    let total: i64 = sqlx::query_scalar("SELECT COUNT(*) FROM storage.blobs")
+        .fetch_one(pool.as_ref())
+        .await
+        .unwrap_or(0);
+
+    {
+        let mut s = state.write().await;
+        s.status = MigrationStatus::Running;
+        s.total_blobs = total as u64;
+        s.migrated_blobs = 0;
+        s.migrated_bytes = 0;
+        s.failed_blobs.clear();
+        s.started_at = Some(chrono::Utc::now());
+        s.completed_at = None;
+    }
+
+    // Stream all hashes+sizes with a cursor.
+    let mut rows =
+        sqlx::query_as::<_, (String, i64)>("SELECT hash, size FROM storage.blobs ORDER BY hash")
+            .fetch(pool.as_ref());
+
+    // Collect all hashes first to avoid holding the cursor across awaits.
+    let mut work: Vec<(String, i64)> = Vec::with_capacity(total as usize);
+    while let Some(row) = rows.next().await {
+        match row {
+            Ok(r) => work.push(r),
+            Err(e) => {
+                tracing::warn!("Error fetching blob row during migration: {}", e);
+            }
+        }
+    }
+
+    // Process in parallel chunks.
+    let results = futures::stream::iter(work.into_iter().map(|(hash, size)| {
+        let src = source.clone();
+        let tgt = target.clone();
+        let st = state.clone();
+        async move {
+            // Check if we should keep running.
+            {
+                let s = st.read().await;
+                if s.status != MigrationStatus::Running {
+                    return;
+                }
+            }
+
+            // Skip if already in target.
+            match tgt.blob_exists(&hash).await {
+                Ok(true) => {
+                    let mut s = st.write().await;
+                    s.migrated_blobs += 1;
+                    s.migrated_bytes += size as u64;
+                    return;
+                }
+                Ok(false) => {}
+                Err(e) => {
+                    tracing::warn!("blob_exists check failed for {}: {}", hash, e);
+                }
+            }
+
+            // Copy: stream from source → temp file → put into target.
+            if let Err(e) = copy_blob(&src, &tgt, &hash).await {
+                tracing::warn!("Failed to migrate blob {}: {}", hash, e);
+                let mut s = st.write().await;
+                s.failed_blobs.push(hash);
+                return;
+            }
+
+            let mut s = st.write().await;
+            s.migrated_blobs += 1;
+            s.migrated_bytes += size as u64;
+        }
+    }))
+    .buffer_unordered(concurrency)
+    .collect::<Vec<()>>()
+    .await;
+
+    drop(results);
+
+    // Finalize state.
+    let mut s = state.write().await;
+    if s.status == MigrationStatus::Running {
+        if s.failed_blobs.is_empty() {
+            s.status = MigrationStatus::Completed;
+        } else {
+            s.status = MigrationStatus::Failed;
+        }
+        s.completed_at = Some(chrono::Utc::now());
+    }
+
+    tracing::info!(
+        "Migration finished: {}/{} blobs, {} failures",
+        s.migrated_blobs,
+        s.total_blobs,
+        s.failed_blobs.len()
+    );
+
+    Ok(())
+}
+
+/// Copy a single blob: stream from source → spool to temp file → put_blob into target.
+async fn copy_blob(
+    source: &Arc<dyn BlobStorageBackend>,
+    target: &Arc<dyn BlobStorageBackend>,
+    hash: &str,
+) -> Result<(), DomainError> {
+    use tokio::io::AsyncWriteExt;
+
+    // Create a temp file to spool content.
+    let tmp_dir = std::env::temp_dir().join("oxicloud-migration");
+    tokio::fs::create_dir_all(&tmp_dir).await.map_err(|e| {
+        DomainError::internal_error("Migration", format!("Failed to create temp dir: {}", e))
+    })?;
+
+    let tmp_path = tmp_dir.join(format!("{}.tmp", hash));
+
+    // Stream from source.
+    let stream = source.get_blob_stream(hash).await?;
+
+    // Write to temp file.
+    let mut file = tokio::fs::File::create(&tmp_path).await.map_err(|e| {
+        DomainError::internal_error("Migration", format!("Failed to create temp file: {}", e))
+    })?;
+
+    let mut stream = std::pin::pin!(stream);
+    while let Some(chunk) = stream.next().await {
+        let bytes = chunk.map_err(|e| {
+            DomainError::internal_error("Migration", format!("Stream error: {}", e))
+        })?;
+        file.write_all(&bytes)
+            .await
+            .map_err(|e| DomainError::internal_error("Migration", format!("Write error: {}", e)))?;
+    }
+    file.flush()
+        .await
+        .map_err(|e| DomainError::internal_error("Migration", format!("Flush error: {}", e)))?;
+    drop(file);
+
+    // Put into target.
+    target.put_blob(hash, &tmp_path).await?;
+
+    // Clean up temp file.
+    let _ = tokio::fs::remove_file(&tmp_path).await;
+
+    Ok(())
+}
+
+/// Verify migration integrity by comparing blob counts and sampling random hashes.
+pub async fn verify_migration(
+    target: Arc<dyn BlobStorageBackend>,
+    pool: Arc<PgPool>,
+    sample_size: usize,
+) -> Result<VerificationResult, DomainError> {
+    // 1. Count blobs in PG.
+    let pg_count: i64 = sqlx::query_scalar("SELECT COUNT(*) FROM storage.blobs")
+        .fetch_one(pool.as_ref())
+        .await
+        .unwrap_or(0);
+
+    // 2. Verify sample of blobs exist in target.
+    let sample_rows: Vec<(String, i64)> =
+        sqlx::query_as("SELECT hash, size FROM storage.blobs ORDER BY random() LIMIT $1")
+            .bind(sample_size as i64)
+            .fetch_all(pool.as_ref())
+            .await
+            .map_err(|e| {
+                DomainError::internal_error("Migration", format!("Sample query failed: {}", e))
+            })?;
+
+    let mut missing = Vec::new();
+    let mut size_mismatches = Vec::new();
+
+    for (hash, expected_size) in &sample_rows {
+        match target.blob_exists(hash).await {
+            Ok(false) => missing.push(hash.clone()),
+            Err(e) => {
+                tracing::warn!("blob_exists failed for {}: {}", hash, e);
+                missing.push(hash.clone());
+            }
+            Ok(true) => {
+                // Verify size matches.
+                if let Ok(actual_size) = target.blob_size(hash).await
+                    && actual_size != *expected_size as u64
+                {
+                    size_mismatches.push(hash.clone());
+                }
+            }
+        }
+    }
+
+    let passed = missing.is_empty() && size_mismatches.is_empty();
+
+    Ok(VerificationResult {
+        pg_blob_count: pg_count as u64,
+        sample_checked: sample_rows.len() as u64,
+        missing_in_target: missing,
+        size_mismatches,
+        passed,
+    })
+}
+
+/// Result of a post-migration integrity check.
+#[derive(Debug, Clone, Serialize, serde::Deserialize)]
+pub struct VerificationResult {
+    pub pg_blob_count: u64,
+    pub sample_checked: u64,
+    pub missing_in_target: Vec<String>,
+    pub size_mismatches: Vec<String>,
+    pub passed: bool,
+}

src/infrastructure/services/mod.rs

@@ -1,18 +1,26 @@
 pub mod audio_metadata_service;
+pub mod azure_blob_backend;
+pub mod cached_blob_backend;
 pub mod chunked_upload_service;
 pub mod compression_service;
 pub mod dedup_service;
+pub mod encrypted_blob_backend;
 pub mod exif_service;
 pub mod file_content_cache;
 pub mod file_system_i18n_service;
 pub mod image_transcode_service;
 pub mod jwt_service;
+pub mod local_blob_backend;
 pub mod login_lockout_service;
+pub mod migration_blob_backend;
+pub mod migration_job;
 pub mod nextcloud_chunked_upload_service;
 pub mod oidc_service;
 pub mod password_hasher;
 pub mod path_resolver_service;
 pub mod path_service;
+pub mod retry_blob_backend;
+pub mod s3_blob_backend;
 pub mod thumbnail_service;
 #[cfg(test)]
 mod thumbnail_service_test;

src/infrastructure/services/retry_blob_backend.rs

@@ -0,0 +1,254 @@
+//! `RetryBlobBackend` — exponential-backoff retry + optional bandwidth throttling
+//! decorator for remote blob backends.
+//!
+//! Wraps any `BlobStorageBackend` and retries transient failures with configurable
+//! exponential backoff.  Optionally throttles upload/download bandwidth via
+//! inter-chunk sleeps.
+
+use std::path::{Path, PathBuf};
+use std::pin::Pin;
+use std::sync::Arc;
+use std::time::Duration;
+
+use crate::application::ports::blob_storage_ports::{
+    BlobStorageBackend, BlobStream, StorageHealthStatus,
+};
+use crate::domain::errors::DomainError;
+
+// ── Retry policy ───────────────────────────────────────────────────
+
+/// Exponential backoff retry configuration.
+#[derive(Debug, Clone)]
+pub struct RetryPolicy {
+    /// Maximum number of retry attempts (0 = no retries).
+    pub max_retries: u32,
+    /// Initial backoff duration before the first retry.
+    pub initial_backoff: Duration,
+    /// Maximum backoff duration (capped).
+    pub max_backoff: Duration,
+    /// Multiplier applied to backoff after each attempt.
+    pub backoff_multiplier: f64,
+}
+
+impl Default for RetryPolicy {
+    fn default() -> Self {
+        Self {
+            max_retries: 3,
+            initial_backoff: Duration::from_millis(100),
+            max_backoff: Duration::from_secs(10),
+            backoff_multiplier: 2.0,
+        }
+    }
+}
+
+// ── RetryBlobBackend ───────────────────────────────────────────────
+
+/// Decorator that retries failed backend operations with exponential backoff.
+pub struct RetryBlobBackend {
+    inner: Arc<dyn BlobStorageBackend>,
+    policy: RetryPolicy,
+}
+
+impl RetryBlobBackend {
+    pub fn new(inner: Arc<dyn BlobStorageBackend>, policy: RetryPolicy) -> Self {
+        Self { inner, policy }
+    }
+}
+
+/// Execute an async closure with exponential backoff retry.
+async fn retry_async<F, Fut, T>(
+    policy: &RetryPolicy,
+    name: &str,
+    mut f: F,
+) -> Result<T, DomainError>
+where
+    F: FnMut() -> Fut,
+    Fut: std::future::Future<Output = Result<T, DomainError>>,
+{
+    let mut attempt = 0u32;
+    let mut backoff = policy.initial_backoff;
+
+    loop {
+        match f().await {
+            Ok(v) => return Ok(v),
+            Err(e) if attempt < policy.max_retries && is_retryable(&e) => {
+                attempt += 1;
+                tracing::warn!(
+                    "Retry {}/{} for {} after error: {} (backoff {:?})",
+                    attempt,
+                    policy.max_retries,
+                    name,
+                    e,
+                    backoff
+                );
+                tokio::time::sleep(backoff).await;
+                let next =
+                    Duration::from_secs_f64(backoff.as_secs_f64() * policy.backoff_multiplier);
+                backoff = next.min(policy.max_backoff);
+            }
+            Err(e) => return Err(e),
+        }
+    }
+}
+
+/// Determine if an error is likely transient (network timeout, 5xx, etc.).
+fn is_retryable(err: &DomainError) -> bool {
+    let msg = err.to_string().to_lowercase();
+    msg.contains("timeout")
+        || msg.contains("connection")
+        || msg.contains("503")
+        || msg.contains("500")
+        || msg.contains("429")
+        || msg.contains("temporarily")
+        || msg.contains("broken pipe")
+        || msg.contains("reset by peer")
+}
+
+impl BlobStorageBackend for RetryBlobBackend {
+    fn initialize(
+        &self,
+    ) -> Pin<Box<dyn std::future::Future<Output = Result<(), DomainError>> + Send + '_>> {
+        let inner = self.inner.clone();
+        let policy = self.policy.clone();
+        Box::pin(async move {
+            retry_async(&policy, "initialize", || {
+                let inner = inner.clone();
+                async move { inner.initialize().await }
+            })
+            .await
+        })
+    }
+
+    fn put_blob(
+        &self,
+        hash: &str,
+        source_path: &Path,
+    ) -> Pin<Box<dyn std::future::Future<Output = Result<u64, DomainError>> + Send + '_>> {
+        let inner = self.inner.clone();
+        let policy = self.policy.clone();
+        let hash = hash.to_string();
+        let path = source_path.to_path_buf();
+        Box::pin(async move {
+            retry_async(&policy, &format!("put_blob({hash})"), || {
+                let inner = inner.clone();
+                let hash = hash.clone();
+                let path = path.clone();
+                async move { inner.put_blob(&hash, &path).await }
+            })
+            .await
+        })
+    }
+
+    fn get_blob_stream(
+        &self,
+        hash: &str,
+    ) -> Pin<Box<dyn std::future::Future<Output = Result<BlobStream, DomainError>> + Send + '_>>
+    {
+        let inner = self.inner.clone();
+        let policy = self.policy.clone();
+        let hash = hash.to_string();
+        Box::pin(async move {
+            retry_async(&policy, &format!("get_blob_stream({hash})"), || {
+                let inner = inner.clone();
+                let hash = hash.clone();
+                async move { inner.get_blob_stream(&hash).await }
+            })
+            .await
+        })
+    }
+
+    fn get_blob_range_stream(
+        &self,
+        hash: &str,
+        start: u64,
+        end: Option<u64>,
+    ) -> Pin<Box<dyn std::future::Future<Output = Result<BlobStream, DomainError>> + Send + '_>>
+    {
+        let inner = self.inner.clone();
+        let policy = self.policy.clone();
+        let hash = hash.to_string();
+        Box::pin(async move {
+            retry_async(&policy, &format!("get_blob_range({hash})"), || {
+                let inner = inner.clone();
+                let hash = hash.clone();
+                async move { inner.get_blob_range_stream(&hash, start, end).await }
+            })
+            .await
+        })
+    }
+
+    fn delete_blob(
+        &self,
+        hash: &str,
+    ) -> Pin<Box<dyn std::future::Future<Output = Result<(), DomainError>> + Send + '_>> {
+        let inner = self.inner.clone();
+        let policy = self.policy.clone();
+        let hash = hash.to_string();
+        Box::pin(async move {
+            retry_async(&policy, &format!("delete_blob({hash})"), || {
+                let inner = inner.clone();
+                let hash = hash.clone();
+                async move { inner.delete_blob(&hash).await }
+            })
+            .await
+        })
+    }
+
+    fn blob_exists(
+        &self,
+        hash: &str,
+    ) -> Pin<Box<dyn std::future::Future<Output = Result<bool, DomainError>> + Send + '_>> {
+        let inner = self.inner.clone();
+        let policy = self.policy.clone();
+        let hash = hash.to_string();
+        Box::pin(async move {
+            retry_async(&policy, &format!("blob_exists({hash})"), || {
+                let inner = inner.clone();
+                let hash = hash.clone();
+                async move { inner.blob_exists(&hash).await }
+            })
+            .await
+        })
+    }
+
+    fn blob_size(
+        &self,
+        hash: &str,
+    ) -> Pin<Box<dyn std::future::Future<Output = Result<u64, DomainError>> + Send + '_>> {
+        let inner = self.inner.clone();
+        let policy = self.policy.clone();
+        let hash = hash.to_string();
+        Box::pin(async move {
+            retry_async(&policy, &format!("blob_size({hash})"), || {
+                let inner = inner.clone();
+                let hash = hash.clone();
+                async move { inner.blob_size(&hash).await }
+            })
+            .await
+        })
+    }
+
+    fn health_check(
+        &self,
+    ) -> Pin<
+        Box<dyn std::future::Future<Output = Result<StorageHealthStatus, DomainError>> + Send + '_>,
+    > {
+        let inner = self.inner.clone();
+        let policy = self.policy.clone();
+        Box::pin(async move {
+            retry_async(&policy, "health_check", || {
+                let inner = inner.clone();
+                async move { inner.health_check().await }
+            })
+            .await
+        })
+    }
+
+    fn backend_type(&self) -> &'static str {
+        "retry"
+    }
+
+    fn local_blob_path(&self, hash: &str) -> Option<PathBuf> {
+        self.inner.local_blob_path(hash)
+    }
+}

src/infrastructure/services/s3_blob_backend.rs

@@ -0,0 +1,344 @@
+//! S3-Compatible Blob Backend — stores blobs in any S3-compatible object store.
+//!
+//! Supports AWS S3, Backblaze B2, Cloudflare R2, MinIO, DigitalOcean Spaces,
+//! Wasabi, and any other service that implements the S3 API.
+
+use aws_sdk_s3::primitives::ByteStream;
+use std::path::{Path, PathBuf};
+use std::pin::Pin;
+use tokio::fs;
+use tokio_util::io::ReaderStream;
+
+use crate::application::ports::blob_storage_ports::{
+    BlobStorageBackend, BlobStream, StorageHealthStatus,
+};
+use crate::common::config::S3StorageConfig;
+use crate::domain::errors::{DomainError, ErrorKind};
+
+/// S3-compatible blob storage backend.
+///
+/// Blobs are stored as objects with key `{2-char-prefix}/{hash}.blob`,
+/// mirroring the local filesystem layout for consistency.
+pub struct S3BlobBackend {
+    client: aws_sdk_s3::Client,
+    bucket: String,
+}
+
+impl S3BlobBackend {
+    /// Build a new S3 backend from configuration.
+    ///
+    /// Supports custom endpoints for non-AWS providers (Backblaze B2,
+    /// MinIO, Cloudflare R2, etc.).
+    pub fn new(config: &S3StorageConfig) -> Self {
+        let credentials = aws_sdk_s3::config::Credentials::new(
+            &config.access_key,
+            &config.secret_key,
+            None,
+            None,
+            "oxicloud",
+        );
+
+        let mut builder = aws_sdk_s3::config::Builder::new()
+            .region(aws_sdk_s3::config::Region::new(config.region.clone()))
+            .credentials_provider(credentials)
+            .behavior_version_latest();
+
+        if let Some(ref endpoint) = config.endpoint_url {
+            builder = builder.endpoint_url(endpoint);
+        }
+
+        if config.force_path_style {
+            builder = builder.force_path_style(true);
+        }
+
+        let client = aws_sdk_s3::Client::from_conf(builder.build());
+
+        Self {
+            client,
+            bucket: config.bucket.clone(),
+        }
+    }
+
+    /// Compute the S3 object key for a given hash.
+    fn object_key(hash: &str) -> String {
+        let prefix = &hash[0..2];
+        format!("{}/{}.blob", prefix, hash)
+    }
+}
+
+impl BlobStorageBackend for S3BlobBackend {
+    fn initialize(
+        &self,
+    ) -> Pin<Box<dyn std::future::Future<Output = Result<(), DomainError>> + Send + '_>> {
+        Box::pin(async move {
+            // Verify bucket exists and is accessible
+            self.client
+                .head_bucket()
+                .bucket(&self.bucket)
+                .send()
+                .await
+                .map_err(|e| {
+                    DomainError::internal_error(
+                        "S3",
+                        format!("Cannot access bucket '{}': {}", self.bucket, e),
+                    )
+                })?;
+
+            tracing::info!("S3 blob backend initialized: bucket={}", self.bucket);
+            Ok(())
+        })
+    }
+
+    fn put_blob(
+        &self,
+        hash: &str,
+        source_path: &Path,
+    ) -> Pin<Box<dyn std::future::Future<Output = Result<u64, DomainError>> + Send + '_>> {
+        let hash = hash.to_owned();
+        let source_path = source_path.to_owned();
+        Box::pin(async move {
+            let key = Self::object_key(&hash);
+
+            // Check if object already exists (idempotent)
+            let exists = self
+                .client
+                .head_object()
+                .bucket(&self.bucket)
+                .key(&key)
+                .send()
+                .await
+                .is_ok();
+
+            if exists {
+                // Blob already in S3 — remove local source and return size
+                let file_size = fs::metadata(&source_path)
+                    .await
+                    .map_err(|e| {
+                        DomainError::internal_error(
+                            "S3",
+                            format!("Failed to stat source file: {}", e),
+                        )
+                    })?
+                    .len();
+                let _ = fs::remove_file(&source_path).await;
+                return Ok(file_size);
+            }
+
+            // Upload from local file
+            let body = ByteStream::from_path(&source_path).await.map_err(|e| {
+                DomainError::internal_error("S3", format!("Failed to read source file: {}", e))
+            })?;
+
+            let file_size = fs::metadata(&source_path)
+                .await
+                .map_err(|e| {
+                    DomainError::internal_error("S3", format!("Failed to stat source file: {}", e))
+                })?
+                .len();
+
+            self.client
+                .put_object()
+                .bucket(&self.bucket)
+                .key(&key)
+                .body(body)
+                .send()
+                .await
+                .map_err(|e| {
+                    DomainError::internal_error(
+                        "S3",
+                        format!("Failed to upload blob {}: {}", hash, e),
+                    )
+                })?;
+
+            // Clean up local source after successful upload
+            let _ = fs::remove_file(&source_path).await;
+
+            Ok(file_size)
+        })
+    }
+
+    fn get_blob_stream(
+        &self,
+        hash: &str,
+    ) -> Pin<Box<dyn std::future::Future<Output = Result<BlobStream, DomainError>> + Send + '_>>
+    {
+        let hash = hash.to_owned();
+        Box::pin(async move {
+            let key = Self::object_key(&hash);
+
+            let output = self
+                .client
+                .get_object()
+                .bucket(&self.bucket)
+                .key(&key)
+                .send()
+                .await
+                .map_err(|e| {
+                    DomainError::new(
+                        ErrorKind::NotFound,
+                        "S3",
+                        format!("Failed to get blob {}: {}", hash, e),
+                    )
+                })?;
+
+            // Convert S3 ByteStream into a Stream<Item = Result<Bytes, io::Error>>
+            // via AsyncRead adapter
+            let reader = output.body.into_async_read();
+            Ok(Box::pin(ReaderStream::with_capacity(reader, 256 * 1024)) as BlobStream)
+        })
+    }
+
+    fn get_blob_range_stream(
+        &self,
+        hash: &str,
+        start: u64,
+        end: Option<u64>,
+    ) -> Pin<Box<dyn std::future::Future<Output = Result<BlobStream, DomainError>> + Send + '_>>
+    {
+        let hash = hash.to_owned();
+        Box::pin(async move {
+            let key = Self::object_key(&hash);
+
+            let range = match end {
+                Some(end_pos) => format!("bytes={}-{}", start, end_pos.saturating_sub(1)),
+                None => format!("bytes={}-", start),
+            };
+
+            let output = self
+                .client
+                .get_object()
+                .bucket(&self.bucket)
+                .key(&key)
+                .range(range)
+                .send()
+                .await
+                .map_err(|e| {
+                    DomainError::new(
+                        ErrorKind::NotFound,
+                        "S3",
+                        format!("Failed to get blob range {}: {}", hash, e),
+                    )
+                })?;
+
+            let reader = output.body.into_async_read();
+            Ok(Box::pin(ReaderStream::with_capacity(reader, 256 * 1024)) as BlobStream)
+        })
+    }
+
+    fn delete_blob(
+        &self,
+        hash: &str,
+    ) -> Pin<Box<dyn std::future::Future<Output = Result<(), DomainError>> + Send + '_>> {
+        let hash = hash.to_owned();
+        Box::pin(async move {
+            let key = Self::object_key(&hash);
+
+            // S3 DeleteObject is already idempotent (returns 204 even if not found)
+            self.client
+                .delete_object()
+                .bucket(&self.bucket)
+                .key(&key)
+                .send()
+                .await
+                .map_err(|e| {
+                    DomainError::internal_error(
+                        "S3",
+                        format!("Failed to delete blob {}: {}", hash, e),
+                    )
+                })?;
+
+            Ok(())
+        })
+    }
+
+    fn blob_exists(
+        &self,
+        hash: &str,
+    ) -> Pin<Box<dyn std::future::Future<Output = Result<bool, DomainError>> + Send + '_>> {
+        let hash = hash.to_owned();
+        Box::pin(async move {
+            let key = Self::object_key(&hash);
+
+            match self
+                .client
+                .head_object()
+                .bucket(&self.bucket)
+                .key(&key)
+                .send()
+                .await
+            {
+                Ok(_) => Ok(true),
+                Err(e) => {
+                    // Check if it's a 404 (not found) vs an actual error
+                    let service_err = e.into_service_error();
+                    if service_err.is_not_found() {
+                        Ok(false)
+                    } else {
+                        Err(DomainError::internal_error(
+                            "S3",
+                            format!("Failed to check blob {}: {}", hash, service_err),
+                        ))
+                    }
+                }
+            }
+        })
+    }
+
+    fn blob_size(
+        &self,
+        hash: &str,
+    ) -> Pin<Box<dyn std::future::Future<Output = Result<u64, DomainError>> + Send + '_>> {
+        let hash = hash.to_owned();
+        Box::pin(async move {
+            let key = Self::object_key(&hash);
+
+            let output = self
+                .client
+                .head_object()
+                .bucket(&self.bucket)
+                .key(&key)
+                .send()
+                .await
+                .map_err(|e| {
+                    DomainError::new(
+                        ErrorKind::NotFound,
+                        "S3",
+                        format!("Failed to stat blob {}: {}", hash, e),
+                    )
+                })?;
+
+            Ok(output.content_length().unwrap_or(0) as u64)
+        })
+    }
+
+    fn health_check(
+        &self,
+    ) -> Pin<
+        Box<dyn std::future::Future<Output = Result<StorageHealthStatus, DomainError>> + Send + '_>,
+    > {
+        Box::pin(async move {
+            match self.client.head_bucket().bucket(&self.bucket).send().await {
+                Ok(_) => Ok(StorageHealthStatus {
+                    connected: true,
+                    backend_type: "s3".to_string(),
+                    message: format!("S3 bucket '{}' is accessible", self.bucket),
+                    available_bytes: None,
+                }),
+                Err(e) => Ok(StorageHealthStatus {
+                    connected: false,
+                    backend_type: "s3".to_string(),
+                    message: format!("S3 bucket '{}' is not accessible: {}", self.bucket, e),
+                    available_bytes: None,
+                }),
+            }
+        })
+    }
+
+    fn backend_type(&self) -> &'static str {
+        "s3"
+    }
+
+    fn local_blob_path(&self, _hash: &str) -> Option<PathBuf> {
+        None // Remote backend — no local path
+    }
+}

src/interfaces/api/handlers/admin_handler.rs

@@ -8,8 +8,9 @@ use axum::{
 
 use crate::application::dtos::settings_dto::{
     AdminCreateUserDto, AdminResetPasswordDto, DashboardStatsDto, ListUsersQueryDto,
-    SaveOidcSettingsDto, TestOidcConnectionDto, UpdateUserActiveDto, UpdateUserQuotaDto,
-    UpdateUserRoleDto,
+    MigrationStateDto, SaveOidcSettingsDto, SaveStorageSettingsDto, StartMigrationDto,
+    TestOidcConnectionDto, TestStorageConnectionDto, UpdateUserActiveDto, UpdateUserQuotaDto,
+    UpdateUserRoleDto, VerifyMigrationDto,
 };
 use crate::application::ports::auth_ports::TokenServicePort;
 use crate::common::di::AppState;
@@ -24,6 +25,22 @@ pub fn admin_routes() -> Router<Arc<AppState>> {
         .route("/settings/oidc", get(get_oidc_settings))
         .route("/settings/oidc", put(save_oidc_settings))
         .route("/settings/oidc/test", post(test_oidc_connection))
+        // Storage settings
+        .route("/settings/storage", get(get_storage_settings))
+        .route("/settings/storage", put(save_storage_settings))
+        .route("/settings/storage/test", post(test_storage_connection))
+        // Storage migration
+        .route("/storage/migration", get(get_migration_status))
+        .route("/storage/migration/start", post(start_migration))
+        .route("/storage/migration/pause", post(pause_migration))
+        .route("/storage/migration/resume", post(resume_migration))
+        .route("/storage/migration/complete", post(complete_migration))
+        .route("/storage/migration/verify", post(verify_migration))
+        // Encryption key generation
+        .route(
+            "/settings/storage/generate-key",
+            post(generate_encryption_key),
+        )
         .route("/settings/general", get(get_general_settings))
         // Dashboard / stats
         .route("/dashboard", get(get_dashboard_stats))
@@ -148,6 +165,336 @@ async fn test_oidc_connection(
     Ok(Json(result))
 }
 
+// ─────────────────────────────────────────────────────
+// Storage settings handlers
+// ─────────────────────────────────────────────────────
+
+/// GET /api/admin/settings/storage — get storage backend settings
+async fn get_storage_settings(
+    State(state): State<Arc<AppState>>,
+    headers: HeaderMap,
+) -> Result<impl IntoResponse, AppError> {
+    admin_guard(&state, &headers).await?;
+
+    let svc = state
+        .storage_settings_service
+        .as_ref()
+        .ok_or_else(|| AppError::internal_error("Storage settings service not available"))?;
+
+    let settings = svc
+        .get_storage_settings()
+        .await
+        .map_err(|e| AppError::internal_error(format!("Failed to load storage settings: {}", e)))?;
+
+    Ok(Json(settings))
+}
+
+/// PUT /api/admin/settings/storage — save storage backend settings
+async fn save_storage_settings(
+    State(state): State<Arc<AppState>>,
+    headers: HeaderMap,
+    Json(dto): Json<SaveStorageSettingsDto>,
+) -> Result<impl IntoResponse, AppError> {
+    let (user_id, _) = admin_guard(&state, &headers).await?;
+
+    let svc = state
+        .storage_settings_service
+        .as_ref()
+        .ok_or_else(|| AppError::internal_error("Storage settings service not available"))?;
+
+    svc.save_storage_settings(dto, user_id)
+        .await
+        .map_err(|e| AppError::internal_error(format!("Failed to save storage settings: {}", e)))?;
+
+    Ok((
+        StatusCode::OK,
+        Json(serde_json::json!({
+            "message": "Storage settings saved successfully"
+        })),
+    ))
+}
+
+/// POST /api/admin/settings/storage/test — test storage backend connection
+async fn test_storage_connection(
+    State(state): State<Arc<AppState>>,
+    headers: HeaderMap,
+    Json(dto): Json<TestStorageConnectionDto>,
+) -> Result<impl IntoResponse, AppError> {
+    admin_guard(&state, &headers).await?;
+
+    let svc = state
+        .storage_settings_service
+        .as_ref()
+        .ok_or_else(|| AppError::internal_error("Storage settings service not available"))?;
+
+    let result = svc
+        .test_storage_connection(dto)
+        .await
+        .map_err(|e| AppError::internal_error(format!("Storage connection test failed: {}", e)))?;
+
+    Ok(Json(result))
+}
+
+// ─────────────────────────────────────────────────────
+// Storage migration handlers
+// ─────────────────────────────────────────────────────
+
+/// GET /api/admin/storage/migration — current migration progress
+async fn get_migration_status(
+    State(state): State<Arc<AppState>>,
+    headers: HeaderMap,
+) -> Result<impl IntoResponse, AppError> {
+    admin_guard(&state, &headers).await?;
+    let s = state.migration_state.read().await;
+    Ok(Json(migration_state_to_dto(&s)))
+}
+
+/// POST /api/admin/storage/migration/start — begin background migration
+async fn start_migration(
+    State(state): State<Arc<AppState>>,
+    headers: HeaderMap,
+    Json(dto): Json<StartMigrationDto>,
+) -> Result<impl IntoResponse, AppError> {
+    use crate::infrastructure::services::migration_blob_backend::MigrationStatus;
+
+    admin_guard(&state, &headers).await?;
+
+    // Check not already running.
+    {
+        let s = state.migration_state.read().await;
+        if s.status == MigrationStatus::Running {
+            return Err(AppError::bad_request("A migration is already running"));
+        }
+    }
+
+    let pool = state
+        .db_pool
+        .clone()
+        .ok_or_else(|| AppError::internal_error("Database not available"))?;
+
+    let source = state.core.dedup_service.backend().clone();
+    let svc = state
+        .storage_settings_service
+        .as_ref()
+        .ok_or_else(|| AppError::internal_error("Storage settings service not available"))?;
+
+    // Build target backend from saved settings.
+    let effective = svc
+        .load_effective_storage_config()
+        .await
+        .map_err(|e| AppError::internal_error(format!("Failed to load storage config: {}", e)))?;
+
+    let target = build_backend_from_config(&effective)
+        .map_err(|e| AppError::internal_error(format!("Failed to build target backend: {}", e)))?;
+    target
+        .initialize()
+        .await
+        .map_err(|e| AppError::internal_error(format!("Target backend init failed: {}", e)))?;
+
+    let concurrency = dto.concurrency.unwrap_or(4).clamp(1, 16);
+    let migration_state = state.migration_state.clone();
+
+    // Spawn the background migration job.
+    tokio::spawn(async move {
+        if let Err(e) = crate::infrastructure::services::migration_job::run_migration(
+            source,
+            target,
+            pool,
+            migration_state,
+            concurrency,
+        )
+        .await
+        {
+            tracing::error!("Migration job error: {}", e);
+        }
+    });
+
+    Ok((
+        StatusCode::OK,
+        Json(serde_json::json!({ "message": "Migration started" })),
+    ))
+}
+
+/// POST /api/admin/storage/migration/pause — pause running migration
+async fn pause_migration(
+    State(state): State<Arc<AppState>>,
+    headers: HeaderMap,
+) -> Result<impl IntoResponse, AppError> {
+    use crate::infrastructure::services::migration_blob_backend::MigrationStatus;
+    admin_guard(&state, &headers).await?;
+
+    let mut s = state.migration_state.write().await;
+    if s.status != MigrationStatus::Running {
+        return Err(AppError::bad_request("No running migration to pause"));
+    }
+    s.status = MigrationStatus::Paused;
+    Ok((
+        StatusCode::OK,
+        Json(serde_json::json!({ "message": "Migration paused" })),
+    ))
+}
+
+/// POST /api/admin/storage/migration/resume — resume paused migration
+async fn resume_migration(
+    State(state): State<Arc<AppState>>,
+    headers: HeaderMap,
+) -> Result<impl IntoResponse, AppError> {
+    use crate::infrastructure::services::migration_blob_backend::MigrationStatus;
+    admin_guard(&state, &headers).await?;
+
+    // Set status back to Running — the background task checks on each blob.
+    let mut s = state.migration_state.write().await;
+    if s.status != MigrationStatus::Paused {
+        return Err(AppError::bad_request("No paused migration to resume"));
+    }
+    s.status = MigrationStatus::Running;
+    Ok((
+        StatusCode::OK,
+        Json(serde_json::json!({ "message": "Migration resumed" })),
+    ))
+}
+
+/// POST /api/admin/storage/migration/complete — finalize migration
+async fn complete_migration(
+    State(state): State<Arc<AppState>>,
+    headers: HeaderMap,
+) -> Result<impl IntoResponse, AppError> {
+    use crate::infrastructure::services::migration_blob_backend::MigrationStatus;
+    admin_guard(&state, &headers).await?;
+
+    let s = state.migration_state.read().await;
+    if s.status != MigrationStatus::Completed {
+        return Err(AppError::bad_request(
+            "Migration must be completed (100%) before finalizing",
+        ));
+    }
+    drop(s);
+
+    // Mark as idle — the admin has acknowledged completion.
+    let mut s = state.migration_state.write().await;
+    s.status = MigrationStatus::Idle;
+
+    Ok((
+        StatusCode::OK,
+        Json(
+            serde_json::json!({ "message": "Migration finalized. Restart the server to use the new backend." }),
+        ),
+    ))
+}
+
+/// POST /api/admin/storage/migration/verify — run integrity check
+async fn verify_migration(
+    State(state): State<Arc<AppState>>,
+    headers: HeaderMap,
+    Json(dto): Json<VerifyMigrationDto>,
+) -> Result<impl IntoResponse, AppError> {
+    admin_guard(&state, &headers).await?;
+
+    let pool = state
+        .db_pool
+        .clone()
+        .ok_or_else(|| AppError::internal_error("Database not available"))?;
+
+    let svc = state
+        .storage_settings_service
+        .as_ref()
+        .ok_or_else(|| AppError::internal_error("Storage settings service not available"))?;
+
+    let effective = svc
+        .load_effective_storage_config()
+        .await
+        .map_err(|e| AppError::internal_error(format!("Failed to load storage config: {}", e)))?;
+
+    let target = build_backend_from_config(&effective)
+        .map_err(|e| AppError::internal_error(format!("Failed to build target backend: {}", e)))?;
+    target
+        .initialize()
+        .await
+        .map_err(|e| AppError::internal_error(format!("Target backend init failed: {}", e)))?;
+
+    let sample_size = dto.sample_size.unwrap_or(100).clamp(1, 1000);
+
+    let result =
+        crate::infrastructure::services::migration_job::verify_migration(target, pool, sample_size)
+            .await
+            .map_err(|e| AppError::internal_error(format!("Verification failed: {}", e)))?;
+
+    Ok(Json(result))
+}
+
+/// Helper: convert MigrationState to DTO for JSON serialization.
+fn migration_state_to_dto(
+    s: &crate::infrastructure::services::migration_blob_backend::MigrationState,
+) -> MigrationStateDto {
+    let throughput = match (s.started_at, s.migrated_bytes) {
+        (Some(start), bytes) if bytes > 0 => {
+            let elapsed = chrono::Utc::now()
+                .signed_duration_since(start)
+                .num_seconds()
+                .max(1) as f64;
+            Some(bytes as f64 / elapsed)
+        }
+        _ => None,
+    };
+
+    MigrationStateDto {
+        status: format!("{:?}", s.status).to_lowercase(),
+        total_blobs: s.total_blobs,
+        migrated_blobs: s.migrated_blobs,
+        migrated_bytes: s.migrated_bytes,
+        failed_blobs: s.failed_blobs.clone(),
+        started_at: s.started_at.map(|d| d.to_rfc3339()),
+        completed_at: s.completed_at.map(|d| d.to_rfc3339()),
+        throughput_bytes_per_sec: throughput,
+    }
+}
+
+/// POST /api/admin/settings/storage/generate-key — generate a random AES-256 key.
+async fn generate_encryption_key(
+    State(state): State<Arc<AppState>>,
+    headers: HeaderMap,
+) -> Result<impl IntoResponse, AppError> {
+    admin_guard(&state, &headers).await?;
+
+    let key =
+        crate::infrastructure::services::encrypted_blob_backend::EncryptedBlobBackend::generate_key(
+        );
+    let key_b64 = base64::Engine::encode(&base64::engine::general_purpose::STANDARD, key);
+
+    Ok(Json(serde_json::json!({
+        "key": key_b64,
+        "warning": "Store this key securely. If lost, encrypted data is IRRECOVERABLY LOST."
+    })))
+}
+
+/// Helper: build a BlobStorageBackend from StorageConfig.
+fn build_backend_from_config(
+    config: &crate::common::config::StorageConfig,
+) -> Result<
+    std::sync::Arc<dyn crate::application::ports::blob_storage_ports::BlobStorageBackend>,
+    String,
+> {
+    match config.backend {
+        crate::common::config::StorageBackendType::Local => Ok(std::sync::Arc::new(
+            crate::infrastructure::services::local_blob_backend::LocalBlobBackend::new(
+                std::path::Path::new(&config.root_dir),
+            ),
+        )),
+        crate::common::config::StorageBackendType::S3 => {
+            let s3 = config.s3.as_ref().ok_or("S3 config missing")?;
+            Ok(std::sync::Arc::new(
+                crate::infrastructure::services::s3_blob_backend::S3BlobBackend::new(s3),
+            ))
+        }
+        crate::common::config::StorageBackendType::Azure => {
+            let az = config.azure.as_ref().ok_or("Azure config missing")?;
+            Ok(std::sync::Arc::new(
+                crate::infrastructure::services::azure_blob_backend::AzureBlobBackend::new(az),
+            ))
+        }
+    }
+}
+
 /// GET /api/admin/settings/general — system overview (backward compat)
 async fn get_general_settings(
     State(state): State<Arc<AppState>>,

static/admin.html

@@ -53,6 +53,9 @@
                     <button class="admin-tab" id="tab-btn-oidc">
                         <i class="fas fa-key"></i> <span data-i18n="admin.tab_oidc">SSO / OIDC</span>
                     </button>
+                    <button class="admin-tab" id="tab-btn-storage">
+                        <i class="fas fa-database"></i> <span data-i18n="admin.tab_storage">Storage</span>
+                    </button>
                 </div>
 
                 <div id="tab-dashboard" class="tab-content active">
@@ -424,6 +427,183 @@
                         </div>
                     </div>
                 </div>
+
+                <!-- ════════ Storage tab ════════ -->
+                <div id="tab-storage" class="tab-content">
+                    <div class="admin-card">
+                        <h2>
+                            <i class="fas fa-database"></i> <span data-i18n="admin.storage_title">Storage Backend</span>
+                        </h2>
+
+                        <!-- Current status -->
+                        <div class="storage-status-grid">
+                            <div class="storage-stat">
+                                <span class="storage-stat__label" data-i18n="admin.storage_current_backend">Active Backend</span>
+                                <span class="storage-stat__value" id="storage-current-backend">—</span>
+                            </div>
+                            <div class="storage-stat">
+                                <span class="storage-stat__label" data-i18n="admin.storage_total_blobs">Total Blobs</span>
+                                <span class="storage-stat__value" id="storage-total-blobs">—</span>
+                            </div>
+                            <div class="storage-stat">
+                                <span class="storage-stat__label" data-i18n="admin.storage_total_size">Total Size</span>
+                                <span class="storage-stat__value" id="storage-total-size">—</span>
+                            </div>
+                            <div class="storage-stat">
+                                <span class="storage-stat__label" data-i18n="admin.storage_dedup_ratio">Dedup Ratio</span>
+                                <span class="storage-stat__value" id="storage-dedup-ratio">—</span>
+                            </div>
+                        </div>
+
+                        <!-- Backend selector -->
+                        <div class="storage-backend-selector">
+                            <label class="storage-backend-option">
+                                <input type="radio" name="storage-backend" value="local" checked />
+                                <span class="storage-backend-option__card">
+                                    <i class="fas fa-hdd"></i>
+                                    <span data-i18n="admin.storage_local">Local Filesystem</span>
+                                </span>
+                            </label>
+                            <label class="storage-backend-option">
+                                <input type="radio" name="storage-backend" value="s3" />
+                                <span class="storage-backend-option__card">
+                                    <i class="fas fa-cloud"></i>
+                                    <span data-i18n="admin.storage_s3">S3-Compatible</span>
+                                </span>
+                            </label>
+                        </div>
+
+                        <!-- S3 form (shown when S3 is selected) -->
+                        <div id="storage-s3-form" class="storage-form" style="display:none">
+                            <!-- Provider preset -->
+                            <div class="form-group">
+                                <label data-i18n="admin.storage_provider_preset">Provider Preset</label>
+                                <select id="storage-preset">
+                                    <option value="custom" data-i18n="admin.storage_preset_custom">Custom</option>
+                                    <option value="aws">Amazon S3</option>
+                                    <option value="backblaze">Backblaze B2</option>
+                                    <option value="cloudflare-r2">Cloudflare R2</option>
+                                    <option value="minio">MinIO</option>
+                                    <option value="digitalocean">DigitalOcean Spaces</option>
+                                    <option value="wasabi">Wasabi</option>
+                                </select>
+                            </div>
+
+                            <!-- Endpoint URL -->
+                            <div class="form-group">
+                                <label><span data-i18n="admin.storage_endpoint_url">Endpoint URL</span>
+                                    <span id="badge-s3_endpoint_url"></span></label>
+                                <input type="url" id="storage-endpoint-url" placeholder="https://s3.amazonaws.com" />
+                                <small data-i18n="admin.storage_endpoint_hint">Leave empty for Amazon S3 default</small>
+                            </div>
+
+                            <!-- Bucket -->
+                            <div class="form-group">
+                                <label><span data-i18n="admin.storage_bucket">Bucket</span>
+                                    <span id="badge-s3_bucket"></span></label>
+                                <input type="text" id="storage-bucket" placeholder="my-oxicloud-bucket" />
+                            </div>
+
+                            <!-- Region -->
+                            <div class="form-group">
+                                <label><span data-i18n="admin.storage_region">Region</span>
+                                    <span id="badge-s3_region"></span></label>
+                                <input type="text" id="storage-region" placeholder="us-east-1" />
+                            </div>
+
+                            <!-- Access Key -->
+                            <div class="form-group">
+                                <label><span data-i18n="admin.storage_access_key">Access Key ID</span>
+                                    <span id="badge-s3_access_key"></span></label>
+                                <input type="text" id="storage-access-key" placeholder="AKIA..." />
+                            </div>
+
+                            <!-- Secret Key -->
+                            <div class="form-group">
+                                <label><span data-i18n="admin.storage_secret_key">Secret Access Key</span>
+                                    <span id="badge-s3_secret_key"></span></label>
+                                <input type="password" id="storage-secret-key" placeholder="Leave empty to keep current value" />
+                                <small id="storage-secret-hint" style="display:none">
+                                    <i class="fas fa-check-circle secret-icon"></i>
+                                    <span data-i18n="admin.storage_secret_configured">A secret key is already configured</span>
+                                </small>
+                            </div>
+
+                            <!-- Force Path Style -->
+                            <div class="toggle-row">
+                                <label data-i18n="admin.storage_path_style">Force Path Style</label>
+                                <label class="switch">
+                                    <input type="checkbox" id="storage-path-style" /><span class="slider"></span>
+                                </label>
+                            </div>
+                            <small data-i18n="admin.storage_path_style_hint">Required for MinIO and some S3-compatible providers</small>
+                        </div>
+
+                        <!-- Action buttons -->
+                        <div class="storage-actions">
+                            <button class="btn btn-secondary" id="btn-test-storage">
+                                <i class="fas fa-vial"></i> <span data-i18n="admin.storage_test_connection">Test Connection</span>
+                            </button>
+                            <button class="btn btn-primary" id="btn-save-storage">
+                                <i class="fas fa-save"></i> <span data-i18n="admin.storage_save">Save</span>
+                            </button>
+                        </div>
+                        <div id="storage-status" class="alert"></div>
+
+                        <!-- Migration section -->
+                        <div class="storage-migration-section">
+                            <h3><i class="fas fa-exchange-alt"></i> <span data-i18n="admin.storage_migration">Backend Migration</span></h3>
+
+                            <!-- Status badge -->
+                            <div class="migration-status-row">
+                                <span data-i18n="admin.migration_status_label">Status:</span>
+                                <span id="migration-status-badge" class="badge badge-migration badge-migration--idle">Idle</span>
+                            </div>
+
+                            <!-- Progress bar (hidden when idle) -->
+                            <div id="migration-progress-section" style="display:none">
+                                <div class="migration-progress-bar">
+                                    <div class="migration-progress-bar__fill" id="migration-progress-fill" style="width:0%"></div>
+                                </div>
+                                <div class="migration-progress-text">
+                                    <span id="migration-progress-label">0 / 0 blobs (0%)</span>
+                                    <span id="migration-throughput"></span>
+                                </div>
+                                <div class="migration-progress-text">
+                                    <span id="migration-bytes-label"></span>
+                                    <span id="migration-eta"></span>
+                                </div>
+                            </div>
+
+                            <!-- Failed blobs (expandable) -->
+                            <details id="migration-failed-section" style="display:none">
+                                <summary><i class="fas fa-exclamation-triangle"></i> <span id="migration-failed-count">0</span> <span data-i18n="admin.migration_failed_blobs">failed blobs</span></summary>
+                                <pre id="migration-failed-list" class="migration-failed-list"></pre>
+                            </details>
+
+                            <!-- Action buttons -->
+                            <div class="migration-actions">
+                                <button class="btn btn-primary" id="btn-start-migration">
+                                    <i class="fas fa-play"></i> <span data-i18n="admin.migration_start">Start Migration</span>
+                                </button>
+                                <button class="btn btn-secondary" id="btn-pause-migration" style="display:none">
+                                    <i class="fas fa-pause"></i> <span data-i18n="admin.migration_pause">Pause</span>
+                                </button>
+                                <button class="btn btn-primary" id="btn-resume-migration" style="display:none">
+                                    <i class="fas fa-play"></i> <span data-i18n="admin.migration_resume">Resume</span>
+                                </button>
+                                <button class="btn btn-secondary" id="btn-verify-migration" style="display:none">
+                                    <i class="fas fa-check-double"></i> <span data-i18n="admin.migration_verify">Verify Integrity</span>
+                                </button>
+                                <button class="btn btn-primary" id="btn-complete-migration" style="display:none">
+                                    <i class="fas fa-flag-checkered"></i> <span data-i18n="admin.migration_complete">Finalize</span>
+                                </button>
+                            </div>
+                            <div id="migration-verify-result" style="display:none"></div>
+                            <div id="migration-status-msg" class="alert" style="display:none"></div>
+                        </div>
+                    </div>
+                </div>
             </div>
         </div>
 

static/css/views/admin.css

@@ -324,6 +324,7 @@ body {
 #oidc-form,
 #secret-hint,
 #password-warning,
+#storage-secret-hint,
 #quota-modal,
 #create-user-modal,
 #reset-pw-modal {
@@ -938,3 +939,176 @@ details[open] summary {
 .btn-danger:hover {
     opacity: 0.88;
 }
+
+/* ── Storage Tab ── */
+
+.storage-status-grid {
+    display: grid;
+    grid-template-columns: repeat(auto-fit, minmax(140px, 1fr));
+    gap: 12px;
+    margin-bottom: 24px;
+}
+.storage-stat {
+    padding: 14px;
+    background: var(--color-bg-hover);
+    border-radius: 12px;
+    text-align: center;
+    border: 1px solid var(--color-border);
+}
+.storage-stat__label {
+    display: block;
+    font-size: 11px;
+    text-transform: uppercase;
+    letter-spacing: 0.5px;
+    color: var(--color-text-secondary);
+    margin-bottom: 4px;
+}
+.storage-stat__value {
+    display: block;
+    font-size: 1.35rem;
+    font-weight: 700;
+    color: var(--color-text-heading);
+}
+
+.storage-backend-selector {
+    display: flex;
+    gap: 12px;
+    margin-bottom: 20px;
+}
+.storage-backend-option {
+    flex: 1;
+    cursor: pointer;
+}
+.storage-backend-option input[type="radio"] {
+    display: none;
+}
+.storage-backend-option__card {
+    display: flex;
+    flex-direction: column;
+    align-items: center;
+    gap: 8px;
+    padding: 18px 14px;
+    border: 2px solid var(--color-border);
+    border-radius: 12px;
+    transition: border-color 0.2s, background 0.2s;
+    text-align: center;
+    font-weight: 500;
+}
+.storage-backend-option__card i {
+    font-size: 1.5rem;
+    color: var(--color-text-secondary);
+    transition: color 0.2s;
+}
+.storage-backend-option input[type="radio"]:checked + .storage-backend-option__card {
+    border-color: var(--color-accent);
+    background: var(--color-accent-subtle);
+}
+.storage-backend-option input[type="radio"]:checked + .storage-backend-option__card i {
+    color: var(--color-accent);
+}
+
+.storage-form {
+    margin-top: 8px;
+}
+
+.storage-actions {
+    display: flex;
+    gap: 10px;
+    margin-top: 24px;
+    justify-content: flex-end;
+}
+
+.storage-migration-section {
+    margin-top: 32px;
+    padding-top: 20px;
+    border-top: 1px solid var(--color-border);
+}
+.storage-migration-section h3 {
+    font-size: 1rem;
+    margin-bottom: 8px;
+    color: var(--color-text-heading);
+}
+.storage-migration-section h3 i {
+    color: var(--color-text-secondary);
+    margin-right: 6px;
+}
+
+/* ── Migration UI ── */
+
+.migration-status-row {
+    display: flex;
+    align-items: center;
+    gap: 8px;
+    margin-bottom: 14px;
+    font-size: 14px;
+}
+
+.badge-migration {
+    padding: 3px 10px;
+    border-radius: 10px;
+    font-size: 12px;
+    font-weight: 600;
+    text-transform: uppercase;
+    letter-spacing: 0.4px;
+}
+.badge-migration--idle {
+    background: var(--color-bg-hover);
+    color: var(--color-text-secondary);
+}
+.badge-migration--running {
+    background: var(--color-accent-subtle);
+    color: var(--color-accent);
+}
+.badge-migration--paused {
+    background: var(--color-warning-bg, #fff8e1);
+    color: var(--color-warning-text, #b28704);
+}
+.badge-migration--completed {
+    background: var(--color-success-bg, #e8f5e9);
+    color: var(--color-success-text, #2e7d32);
+}
+.badge-migration--failed {
+    background: var(--color-danger-bg, #fce4ec);
+    color: var(--color-danger-text, #c62828);
+}
+
+.migration-progress-bar {
+    width: 100%;
+    height: 10px;
+    background: var(--color-bg-hover);
+    border-radius: 6px;
+    overflow: hidden;
+    margin-bottom: 6px;
+}
+.migration-progress-bar__fill {
+    height: 100%;
+    background: var(--color-accent);
+    border-radius: 6px;
+    transition: width 0.3s ease;
+}
+
+.migration-progress-text {
+    display: flex;
+    justify-content: space-between;
+    font-size: 12px;
+    color: var(--color-text-secondary);
+    margin-bottom: 4px;
+}
+
+.migration-failed-list {
+    max-height: 150px;
+    overflow-y: auto;
+    font-size: 11px;
+    background: var(--color-bg-hover);
+    padding: 8px 12px;
+    border-radius: 8px;
+    border: 1px solid var(--color-border);
+    margin-top: 6px;
+}
+
+.migration-actions {
+    display: flex;
+    gap: 10px;
+    margin-top: 16px;
+    flex-wrap: wrap;
+}

static/js/views/admin/admin.js

@@ -138,6 +138,7 @@ function switchTab(name, el) {
     activeTabName = name;
     if (name === 'users') loadUsers();
     if (name === 'dashboard') loadDashboard();
+    if (name === 'storage') loadStorage();
 }
 
 async function loadDashboard() {
@@ -693,6 +694,353 @@ async function saveOidcSettings() {
     btn.innerHTML = `<i class="fas fa-save"></i> ${escapeHtml(t('admin.save_btn'))}`;
 }
 
+/* ── Storage tab ── */
+
+const STORAGE_PRESETS = {
+    'custom':        { endpoint: '',                                    region: '',            pathStyle: false },
+    'aws':           { endpoint: '',                                    region: 'us-east-1',   pathStyle: false },
+    'backblaze':     { endpoint: 'https://s3.{region}.backblazeb2.com', region: 'us-west-004', pathStyle: false },
+    'cloudflare-r2': { endpoint: 'https://{accountId}.r2.cloudflarestorage.com', region: 'auto', pathStyle: true },
+    'minio':         { endpoint: 'http://localhost:9000',               region: 'us-east-1',   pathStyle: true },
+    'digitalocean':  { endpoint: 'https://{region}.digitaloceanspaces.com', region: 'nyc3',    pathStyle: false },
+    'wasabi':        { endpoint: 'https://s3.{region}.wasabisys.com',   region: 'us-east-1',   pathStyle: false },
+};
+
+function toggleS3Form(visible) {
+    if (visible) showElement('storage-s3-form');
+    else hideElement('storage-s3-form');
+}
+
+function onStoragePresetChange() {
+    const preset = document.getElementById('storage-preset').value;
+    const p = STORAGE_PRESETS[preset];
+    if (!p) return;
+    if (p.endpoint) document.getElementById('storage-endpoint-url').value = p.endpoint;
+    if (p.region) document.getElementById('storage-region').value = p.region;
+    document.getElementById('storage-path-style').checked = p.pathStyle;
+}
+
+function showStorageStatus(msg, type) {
+    const el = document.getElementById('storage-status');
+    el.textContent = msg;
+    el.className = `alert alert-${type}`;
+}
+
+async function loadStorage() {
+    try {
+        const resp = await fetch(`${API}/admin/settings/storage`, {
+            headers: headers(),
+            credentials: 'same-origin'
+        });
+        if (!resp.ok) return;
+        const s = await resp.json();
+
+        // Backend selector
+        document.querySelectorAll('input[name="storage-backend"]').forEach((r) => {
+            r.checked = r.value === s.backend;
+        });
+        toggleS3Form(s.backend === 's3');
+
+        // S3 fields
+        document.getElementById('storage-endpoint-url').value = s.s3_endpoint_url || '';
+        document.getElementById('storage-bucket').value = s.s3_bucket || '';
+        document.getElementById('storage-region').value = s.s3_region || '';
+        document.getElementById('storage-access-key').value = '';
+        document.getElementById('storage-secret-key').value = '';
+        document.getElementById('storage-path-style').checked = s.s3_force_path_style;
+
+        // Secret hints
+        if (s.s3_access_key_set) {
+            document.getElementById('storage-access-key').placeholder = t('admin.storage_key_placeholder') || 'Leave empty to keep current value';
+        }
+        if (s.s3_secret_key_set) {
+            showElement('storage-secret-hint');
+        } else {
+            hideElement('storage-secret-hint');
+        }
+
+        // ENV badges
+        (s.env_overrides || []).forEach((field) => {
+            const badge = document.getElementById(`badge-${field}`);
+            if (badge) badge.innerHTML = '<span class="badge badge-env">ENV</span>';
+        });
+
+        // Status section
+        document.getElementById('storage-current-backend').textContent = s.current_backend || '—';
+        document.getElementById('storage-total-blobs').textContent = s.total_blobs != null ? s.total_blobs.toLocaleString() : '—';
+        document.getElementById('storage-total-size').textContent = s.total_bytes_stored != null ? formatBytes(s.total_bytes_stored) : '—';
+        document.getElementById('storage-dedup-ratio').textContent = s.dedup_ratio != null ? `${s.dedup_ratio.toFixed(2)}x` : '—';
+    } catch (e) {
+        showStorageStatus(t('admin.error_network', { message: e.message }), 'error');
+    }
+
+    // Also load migration status
+    loadMigrationStatus();
+}
+
+async function saveStorageSettings() {
+    const btn = document.getElementById('btn-save-storage');
+    btn.disabled = true;
+    btn.innerHTML = `<i class="fas fa-spinner fa-spin"></i> ${escapeHtml(t('admin.saving'))}`;
+
+    const backend = document.querySelector('input[name="storage-backend"]:checked').value;
+    const body = {
+        backend,
+        s3_endpoint_url: document.getElementById('storage-endpoint-url').value.trim() || null,
+        s3_bucket: document.getElementById('storage-bucket').value.trim() || null,
+        s3_region: document.getElementById('storage-region').value.trim() || null,
+        s3_access_key: document.getElementById('storage-access-key').value || null,
+        s3_secret_key: document.getElementById('storage-secret-key').value || null,
+        s3_force_path_style: document.getElementById('storage-path-style').checked
+    };
+
+    try {
+        const resp = await fetch(`${API}/admin/settings/storage`, {
+            method: 'PUT',
+            headers: headers(),
+            credentials: 'same-origin',
+            body: JSON.stringify(body)
+        });
+        if (resp.ok) {
+            showStorageStatus(t('admin.storage_saved') || 'Storage settings saved successfully', 'success');
+            loadStorage();
+        } else {
+            const e = await resp.json().catch(() => ({}));
+            showStorageStatus(`Error: ${e.message || resp.statusText}`, 'error');
+        }
+    } catch (e) {
+        showStorageStatus(t('admin.error_network', { message: e.message }), 'error');
+    }
+    btn.disabled = false;
+    btn.innerHTML = `<i class="fas fa-save"></i> ${escapeHtml(t('admin.storage_save') || 'Save')}`;
+}
+
+async function testStorageConnection() {
+    const btn = document.getElementById('btn-test-storage');
+    btn.disabled = true;
+    btn.innerHTML = `<i class="fas fa-spinner fa-spin"></i> ${escapeHtml(t('admin.testing') || 'Testing...')}`;
+
+    const backend = document.querySelector('input[name="storage-backend"]:checked').value;
+    const body = {
+        backend,
+        s3_endpoint_url: document.getElementById('storage-endpoint-url').value.trim() || null,
+        s3_bucket: document.getElementById('storage-bucket').value.trim() || null,
+        s3_region: document.getElementById('storage-region').value.trim() || null,
+        s3_access_key: document.getElementById('storage-access-key').value || null,
+        s3_secret_key: document.getElementById('storage-secret-key').value || null,
+        s3_force_path_style: document.getElementById('storage-path-style').checked
+    };
+
+    try {
+        const resp = await fetch(`${API}/admin/settings/storage/test`, {
+            method: 'POST',
+            headers: headers(),
+            credentials: 'same-origin',
+            body: JSON.stringify(body)
+        });
+        const r = await resp.json();
+        if (r.connected) {
+            let msg = `${t('admin.storage_test_success') || 'Connection successful'} (${escapeHtml(r.backend_type)})`;
+            if (r.available_bytes != null) msg += ` — ${formatBytes(r.available_bytes)} available`;
+            showStorageStatus(msg, 'success');
+        } else {
+            showStorageStatus(`${t('admin.storage_test_failure') || 'Connection failed'}: ${escapeHtml(r.message)}`, 'error');
+        }
+    } catch (e) {
+        showStorageStatus(t('admin.error_network', { message: e.message }), 'error');
+    }
+    btn.disabled = false;
+    btn.innerHTML = `<i class="fas fa-vial"></i> ${escapeHtml(t('admin.storage_test_connection') || 'Test Connection')}`;
+}
+
+/* ── Migration ── */
+
+let migrationPollTimer = null;
+
+function showMigrationMsg(msg, type) {
+    const el = document.getElementById('migration-status-msg');
+    el.textContent = msg;
+    el.className = `alert alert-${type}`;
+    el.style.display = '';
+}
+
+function updateMigrationUI(m) {
+    // Status badge
+    const badge = document.getElementById('migration-status-badge');
+    badge.textContent = (m.status || 'idle').charAt(0).toUpperCase() + (m.status || 'idle').slice(1);
+    badge.className = `badge badge-migration badge-migration--${m.status || 'idle'}`;
+
+    const isActive = m.status === 'running' || m.status === 'paused';
+    const isCompleted = m.status === 'completed';
+
+    // Progress section
+    const progressSection = document.getElementById('migration-progress-section');
+    progressSection.style.display = (isActive || isCompleted) ? '' : 'none';
+
+    if (m.total_blobs > 0) {
+        const pct = Math.round((m.migrated_blobs / m.total_blobs) * 100);
+        document.getElementById('migration-progress-fill').style.width = `${pct}%`;
+        document.getElementById('migration-progress-label').textContent =
+            `${m.migrated_blobs.toLocaleString()} / ${m.total_blobs.toLocaleString()} blobs (${pct}%)`;
+        document.getElementById('migration-bytes-label').textContent =
+            `${formatBytes(m.migrated_bytes)} transferred`;
+
+        if (m.throughput_bytes_per_sec && m.status === 'running') {
+            document.getElementById('migration-throughput').textContent =
+                `${formatBytes(Math.round(m.throughput_bytes_per_sec))}/s`;
+            const remaining = m.total_blobs - m.migrated_blobs;
+            if (remaining > 0 && m.throughput_bytes_per_sec > 0) {
+                const avgBlobSize = m.migrated_bytes / Math.max(m.migrated_blobs, 1);
+                const etaSecs = Math.round((remaining * avgBlobSize) / m.throughput_bytes_per_sec);
+                const etaMin = Math.ceil(etaSecs / 60);
+                document.getElementById('migration-eta').textContent =
+                    `~${etaMin} min remaining`;
+            }
+        } else {
+            document.getElementById('migration-throughput').textContent = '';
+            document.getElementById('migration-eta').textContent = '';
+        }
+    }
+
+    // Failed blobs section
+    const failedSection = document.getElementById('migration-failed-section');
+    if (m.failed_blobs && m.failed_blobs.length > 0) {
+        failedSection.style.display = '';
+        document.getElementById('migration-failed-count').textContent = m.failed_blobs.length;
+        document.getElementById('migration-failed-list').textContent = m.failed_blobs.join('\n');
+    } else {
+        failedSection.style.display = 'none';
+    }
+
+    // Button visibility
+    document.getElementById('btn-start-migration').style.display =
+        (!isActive && !isCompleted) ? '' : 'none';
+    document.getElementById('btn-pause-migration').style.display =
+        m.status === 'running' ? '' : 'none';
+    document.getElementById('btn-resume-migration').style.display =
+        m.status === 'paused' ? '' : 'none';
+    document.getElementById('btn-verify-migration').style.display =
+        isCompleted ? '' : 'none';
+    document.getElementById('btn-complete-migration').style.display =
+        isCompleted ? '' : 'none';
+}
+
+async function loadMigrationStatus() {
+    try {
+        const resp = await fetch(`${API}/admin/storage/migration`, {
+            headers: headers(),
+            credentials: 'same-origin'
+        });
+        if (!resp.ok) return;
+        const m = await resp.json();
+        updateMigrationUI(m);
+
+        // Auto-poll while running
+        if (m.status === 'running') {
+            if (!migrationPollTimer) {
+                migrationPollTimer = setInterval(loadMigrationStatus, 2000);
+            }
+        } else if (migrationPollTimer) {
+            clearInterval(migrationPollTimer);
+            migrationPollTimer = null;
+        }
+    } catch (_e) { /* ignore */ }
+}
+
+async function startMigration() {
+    const btn = document.getElementById('btn-start-migration');
+    btn.disabled = true;
+    try {
+        const resp = await fetch(`${API}/admin/storage/migration/start`, {
+            method: 'POST',
+            headers: headers(),
+            credentials: 'same-origin',
+            body: JSON.stringify({ concurrency: 4 })
+        });
+        if (resp.ok) {
+            showMigrationMsg(t('admin.migration_started') || 'Migration started', 'success');
+            loadMigrationStatus();
+        } else {
+            const e = await resp.json().catch(() => ({}));
+            showMigrationMsg(`Error: ${e.message || resp.statusText}`, 'error');
+        }
+    } catch (e) {
+        showMigrationMsg(t('admin.error_network', { message: e.message }), 'error');
+    }
+    btn.disabled = false;
+}
+
+async function pauseMigration() {
+    try {
+        const resp = await fetch(`${API}/admin/storage/migration/pause`, {
+            method: 'POST', headers: headers(), credentials: 'same-origin'
+        });
+        if (resp.ok) {
+            showMigrationMsg(t('admin.migration_paused_msg') || 'Migration paused', 'success');
+            loadMigrationStatus();
+        }
+    } catch (_e) { /* ignore */ }
+}
+
+async function resumeMigration() {
+    try {
+        const resp = await fetch(`${API}/admin/storage/migration/resume`, {
+            method: 'POST', headers: headers(), credentials: 'same-origin'
+        });
+        if (resp.ok) {
+            showMigrationMsg(t('admin.migration_resumed_msg') || 'Migration resumed', 'success');
+            loadMigrationStatus();
+        }
+    } catch (_e) { /* ignore */ }
+}
+
+async function verifyMigration() {
+    const btn = document.getElementById('btn-verify-migration');
+    btn.disabled = true;
+    btn.innerHTML = `<i class="fas fa-spinner fa-spin"></i> ${escapeHtml(t('admin.migration_verifying') || 'Verifying...')}`;
+    const resultDiv = document.getElementById('migration-verify-result');
+    try {
+        const resp = await fetch(`${API}/admin/storage/migration/verify`, {
+            method: 'POST',
+            headers: headers(),
+            credentials: 'same-origin',
+            body: JSON.stringify({ sample_size: 100 })
+        });
+        const r = await resp.json();
+        resultDiv.style.display = '';
+        if (r.passed) {
+            resultDiv.innerHTML = `<div class="discovery-result ok"><strong><i class="fas fa-check-circle"></i> ${escapeHtml(t('admin.migration_verify_passed') || 'Verification passed')}</strong><p>${r.sample_checked} blobs checked, ${r.pg_blob_count} total in database</p></div>`;
+        } else {
+            const issues = [];
+            if (r.missing_in_target.length) issues.push(`${r.missing_in_target.length} missing`);
+            if (r.size_mismatches.length) issues.push(`${r.size_mismatches.length} size mismatches`);
+            resultDiv.innerHTML = `<div class="discovery-result fail"><strong><i class="fas fa-times-circle"></i> ${escapeHtml(t('admin.migration_verify_failed') || 'Verification failed')}</strong><p>${issues.join(', ')}</p></div>`;
+        }
+    } catch (e) {
+        resultDiv.style.display = '';
+        resultDiv.innerHTML = `<div class="discovery-result fail"><i class="fas fa-times-circle"></i> Error: ${escapeHtml(e.message)}</div>`;
+    }
+    btn.disabled = false;
+    btn.innerHTML = `<i class="fas fa-check-double"></i> ${escapeHtml(t('admin.migration_verify') || 'Verify Integrity')}`;
+}
+
+async function completeMigration() {
+    try {
+        const resp = await fetch(`${API}/admin/storage/migration/complete`, {
+            method: 'POST', headers: headers(), credentials: 'same-origin'
+        });
+        if (resp.ok) {
+            showMigrationMsg(t('admin.migration_completed_msg') || 'Migration finalized. Restart the server to use the new backend.', 'success');
+            loadMigrationStatus();
+        } else {
+            const e = await resp.json().catch(() => ({}));
+            showMigrationMsg(`Error: ${e.message || resp.statusText}`, 'error');
+        }
+    } catch (e) {
+        showMigrationMsg(t('admin.error_network', { message: e.message }), 'error');
+    }
+}
+
 async function init() {
     try {
         const me = await fetch(`${API}/auth/me`, {
@@ -775,6 +1123,9 @@ document.getElementById('tab-btn-users').addEventListener('click', function () {
 document.getElementById('tab-btn-oidc').addEventListener('click', function () {
     switchTab('oidc', this);
 });
+document.getElementById('tab-btn-storage').addEventListener('click', function () {
+    switchTab('storage', this);
+});
 
 document.getElementById('ds-registration').addEventListener('change', function () {
     toggleRegistration(this.checked);
@@ -797,3 +1148,20 @@ document.getElementById('cu-submit').addEventListener('click', submitCreateUser)
 
 document.getElementById('btn-close-reset-pw').addEventListener('click', closeResetPasswordModal);
 document.getElementById('rp-submit').addEventListener('click', submitResetPassword);
+
+/* ── Storage event listeners ── */
+document.querySelectorAll('input[name="storage-backend"]').forEach((r) => {
+    r.addEventListener('change', function () {
+        toggleS3Form(this.value === 's3');
+    });
+});
+document.getElementById('storage-preset').addEventListener('change', onStoragePresetChange);
+document.getElementById('btn-test-storage').addEventListener('click', testStorageConnection);
+document.getElementById('btn-save-storage').addEventListener('click', saveStorageSettings);
+
+/* ── Migration event listeners ── */
+document.getElementById('btn-start-migration').addEventListener('click', startMigration);
+document.getElementById('btn-pause-migration').addEventListener('click', pauseMigration);
+document.getElementById('btn-resume-migration').addEventListener('click', resumeMigration);
+document.getElementById('btn-verify-migration').addEventListener('click', verifyMigration);
+document.getElementById('btn-complete-migration').addEventListener('click', completeMigration);

static/locales/en.json

@@ -566,7 +566,50 @@
         "error_password_short": "Password must be at least 8 characters",
         "error_generic": "Failed",
         "error_network": "Network error: {{message}}",
-        "error_create_user": "Failed to create user"
+        "error_create_user": "Failed to create user",
+        "tab_storage": "Storage",
+        "storage_title": "Storage Backend",
+        "storage_current_backend": "Active Backend",
+        "storage_total_blobs": "Total Blobs",
+        "storage_total_size": "Total Size",
+        "storage_dedup_ratio": "Dedup Ratio",
+        "storage_backend": "Backend Type",
+        "storage_local": "Local Filesystem",
+        "storage_s3": "S3-Compatible",
+        "storage_provider_preset": "Provider Preset",
+        "storage_preset_custom": "Custom",
+        "storage_endpoint_url": "Endpoint URL",
+        "storage_endpoint_hint": "Leave empty for Amazon S3 default",
+        "storage_bucket": "Bucket",
+        "storage_region": "Region",
+        "storage_access_key": "Access Key ID",
+        "storage_secret_key": "Secret Access Key",
+        "storage_secret_configured": "A secret key is already configured",
+        "storage_key_placeholder": "Leave empty to keep current value",
+        "storage_path_style": "Force Path Style",
+        "storage_path_style_hint": "Required for MinIO and some S3-compatible providers",
+        "storage_test_connection": "Test Connection",
+        "storage_test_success": "Connection successful",
+        "storage_test_failure": "Connection failed",
+        "storage_save": "Save",
+        "storage_saved": "Storage settings saved successfully",
+        "storage_migration": "Backend Migration",
+        "storage_migration_coming_soon": "Backend migration will be available in a future update.",
+        "migration_status_label": "Status:",
+        "migration_start": "Start Migration",
+        "migration_pause": "Pause",
+        "migration_resume": "Resume",
+        "migration_verify": "Verify Integrity",
+        "migration_complete": "Finalize",
+        "migration_started": "Migration started",
+        "migration_paused_msg": "Migration paused",
+        "migration_resumed_msg": "Migration resumed",
+        "migration_completed_msg": "Migration finalized. Restart the server to use the new backend.",
+        "migration_verifying": "Verifying…",
+        "migration_verify_passed": "Verification passed",
+        "migration_verify_failed": "Verification failed",
+        "migration_failed_blobs": "failed blobs",
+        "testing": "Testing…"
     },
     "profile": {
         "page_title": "Profile",

static/locales/es.json

@@ -566,7 +566,50 @@
         "error_password_short": "La contraseña debe tener al menos 8 caracteres",
         "error_generic": "Error",
         "error_network": "Error de red: {{message}}",
-        "error_create_user": "Error al crear usuario"
+        "error_create_user": "Error al crear usuario",
+        "tab_storage": "Almacenamiento",
+        "storage_title": "Backend de Almacenamiento",
+        "storage_current_backend": "Backend Activo",
+        "storage_total_blobs": "Total de Blobs",
+        "storage_total_size": "Tamaño Total",
+        "storage_dedup_ratio": "Ratio de Dedup",
+        "storage_backend": "Tipo de Backend",
+        "storage_local": "Sistema de Archivos Local",
+        "storage_s3": "Compatible con S3",
+        "storage_provider_preset": "Proveedor Preconfigurado",
+        "storage_preset_custom": "Personalizado",
+        "storage_endpoint_url": "URL del Endpoint",
+        "storage_endpoint_hint": "Dejar vacío para usar Amazon S3 por defecto",
+        "storage_bucket": "Bucket",
+        "storage_region": "Región",
+        "storage_access_key": "Access Key ID",
+        "storage_secret_key": "Secret Access Key",
+        "storage_secret_configured": "Ya hay una clave secreta configurada",
+        "storage_key_placeholder": "Dejar vacío para mantener el valor actual",
+        "storage_path_style": "Forzar Path Style",
+        "storage_path_style_hint": "Requerido para MinIO y algunos proveedores compatibles con S3",
+        "storage_test_connection": "Probar Conexión",
+        "storage_test_success": "Conexión exitosa",
+        "storage_test_failure": "Conexión fallida",
+        "storage_save": "Guardar",
+        "storage_saved": "Configuración de almacenamiento guardada correctamente",
+        "storage_migration": "Migración de Backend",
+        "storage_migration_coming_soon": "La migración de backend estará disponible en una futura actualización.",
+        "migration_status_label": "Estado:",
+        "migration_start": "Iniciar Migración",
+        "migration_pause": "Pausar",
+        "migration_resume": "Reanudar",
+        "migration_verify": "Verificar Integridad",
+        "migration_complete": "Finalizar",
+        "migration_started": "Migración iniciada",
+        "migration_paused_msg": "Migración pausada",
+        "migration_resumed_msg": "Migración reanudada",
+        "migration_completed_msg": "Migración finalizada. Reinicia el servidor para usar el nuevo backend.",
+        "migration_verifying": "Verificando…",
+        "migration_verify_passed": "Verificación exitosa",
+        "migration_verify_failed": "Verificación fallida",
+        "migration_failed_blobs": "blobs fallidos",
+        "testing": "Probando…"
     },
     "profile": {
         "page_title": "Perfil",