Update FAQ.md

FAQ.md

@@ -113,6 +113,44 @@ To upgrade to `large disk` version,
 * start master with a larger volume size limit
 * start volume servers, with reasonable maximum number of volumes
 
+**What's the difference between `large_disk` and `large_disk_full`?**
+
+- **`large_disk`**: Normal volumes are limited to 30GB each. This `large_disk` build enables support for volumes larger than 30GB (the `5BytesOffset` flag). It uses 17 bytes per file entry instead of 16 bytes, allowing volume sizes up to 8TB. 
+
+- **`large_disk_full`**: This build includes everything in `large_disk`, PLUS additional filer store backend integrations:
+  - **elastic** - Elasticsearch filer store
+  - **gocdk** - Go Cloud Development Kit support (for cloud storage backends)
+  - **rclone** - Rclone integration for remote storage
+  - **sqlite** - SQLite filer store
+  - **tarantool** - Tarantool filer store
+  - **tikv** - TiKV filer store
+  - **ydb** - YDB (Yandex Database) filer store
+
+  This build is only available for `linux/amd64` due to build complexity.
+
+**Which one should I use?**
+
+- Use the **standard (no suffix)** build if your total storage needs are under 30GB per volume and you don't need extra backends.
+- Use **`_large_disk`** if you need larger volumes (>30GB each) but don't need the extra filer store backends.
+- Use **`_full`** if you need extra filer store backends but don't need large volumes.
+- Use **`_large_disk_full`** if you need both large volumes AND extra filer store backends.
+- Use **`_large_disk_rocksdb`** if you specifically need RocksDB as a filer store with large disk support.
+
+**Example Docker commands:**
+
+```bash
+# Standard build
+docker run chrislusf/seaweedfs:latest server
+
+# Large disk build
+docker run chrislusf/seaweedfs:3.79_large_disk server
+
+# Large disk with full backend support
+docker run chrislusf/seaweedfs:3.79_large_disk_full server
+```
+
+**Important:** The `large_disk` versions are NOT compatible with standard 30GB versions. You cannot mix them in the same cluster. See the section above for migration instructions.
+
 ### How large should I configure the volumes?
 
 If the system has lots of updates or deletions, it is better to keep the volume size small to reduce compaction load.