Add Migrate Between Filer Stores page

Filer-Stores.md

@@ -32,7 +32,7 @@ The Filer Store persists all file metadata and directory information.
 
 #### Switching between different Stores
 It is easy to switch between different filer stores.  
-This is useful if you started with embedded DB and want to move to distributed one or in reverse.
+This is useful if you started with embedded DB and want to move to distributed one or in reverse. See [[Migrate Between Filer Stores]] for all options, including online migration.
 
 For example:
 ```sh

Migrate-Between-Filer-Stores.md

@@ -0,0 +1,76 @@
+How to move the filer metadata from one filer store to another, e.g. from embedded LevelDB to a distributed store such as Redis, MySQL or Cassandra, or the other way around.
+
+Only metadata lives in the filer store: directory entries and the file id references pointing to chunks on the volume servers. The file content never moves, so a filer store migration is just a metadata copy plus a `filer.toml` change.
+
+Pick one of the following options.
+
+## Option 1: Offline migration with fs.meta.save / fs.meta.load
+
+Simple and works between any two store types. Requires a short write stop.
+
+1. Make sure no files are created or modified, then save all metadata:
+
+   ```sh
+   weed shell
+   > fs.meta.save -o backup.meta.gz /
+   ```
+
+   The output reports the number of directories and files saved.
+
+2. Stop the filer.
+
+3. Update `filer.toml` to the new store (see `weed scaffold -config=filer` for a template) and restart the filer.
+
+4. Load the saved metadata:
+
+   ```sh
+   weed shell
+   > fs.meta.load -concurrency=8 backup.meta.gz
+   ```
+
+   * `-concurrency=N` parallelizes file entry creation. Caution: this may not work correctly with some stores such as Redis — use `-concurrency=1` there.
+   * `-dirPrefix=/buckets/important` loads only a subtree.
+
+5. Verify:
+
+   ```sh
+   weed shell
+   > fs.ls -l /
+   > fs.verify /
+   ```
+
+   The saved `.meta` file also serves as a rollback backup.
+
+## Option 2: Online migration with weed filer.meta.backup
+
+`weed filer.meta.backup` continuously copies metadata changes into a different filer store — see [[Async Filer Metadata Backup]].
+
+1. Create `backup_filer.toml` with the new store enabled, configured the same way as `filer.toml`.
+
+2. Start the backup:
+
+   ```sh
+   weed filer.meta.backup -config=/path/to/backup_filer.toml -filer="localhost:8888"
+   ```
+
+   On the first run it traverses all existing metadata, then streams new changes. Progress is checkpointed in the new store, so it can be stopped and resumed at any time. `-restart` forces a fresh full copy. `-filerDir`, `-includePrefixes` and `-excludePrefixes` limit the scope.
+
+3. Cut over once the backup has caught up (the log shows the timestamp it has progressed to):
+   * briefly stop writes to the filer
+   * point `filer.toml` at the new store and restart the filer
+   * resume writes
+
+## Option 3: Add a filer on the new embedded store
+
+Since 2.77, filers discover each other via the master and automatically synchronize metadata — see [[Filer Store Replication]]. If the old and new stores are both embedded stores (leveldb, rocksdb, sqlite), just start a second filer configured with the new store, wait for it to catch up, then shut down the old filer.
+
+Caveats:
+
+* This only works between embedded stores. A pair of a shared store (mysql, redis, ...) and an embedded store does not replicate, and neither do two different shared stores.
+* Replicated embedded filers are eventually consistent.
+* `weed filer.sync` does not work well with multiple `filer.store.id`s.
+
+## Notes
+
+* Only metadata is copied. All chunk references stay valid; nothing on the volume servers changes.
+* Filer stores differ in atomic directory renaming, native TTL, and fast bucket deletion — check the [[Filer Stores]] table before picking the target store.

Migrate-to-Filer-Store.md

@@ -1,3 +1,5 @@
+This page is about copying existing files into SeaweedFS. To migrate the metadata from one filer store to another, see [[Migrate Between Filer Stores]].
+
 If there are already a lot of files, how to move them to the SeaweedFS the most efficient way?
 
 ### 1. Setup Filer

_Sidebar.md

@@ -52,6 +52,7 @@
 
 ### Advanced Filer Configurations
 * [[Migrate to Filer Store]]
+* [[Migrate Between Filer Stores]]
 * [[Add New Filer Store|Customize Filer Store]]
 * [[Filer Store Replication]]
 * [[Filer Active Active cross cluster continuous synchronization]]