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+### Comparing Storage Options
+
+The Filer Store persists all file metadata and directory information.
+
+| Filer Store Name | Lookup | number of entries in a folder | Scalability | Renaming | TTL | Note |
+| ---------------- | -- | -- | -- | -- | -- | -- |
+| memory       | O(1)   | limited by memory | Local, Fast                | | | for testing only, no persistent storage |
+| leveldb      | O(logN)| unlimited | Local, Very Fast               | | | Default, fairly scalable |
+| leveldb2     | O(logN)| unlimited | Local, Very Fast, faster than leveldb          | | | Similar to leveldb, part of the lookup key is 128bit MD5 instead of the long full file path |
+| Redis        | O(1)   | limited   | Local or Distributed, Fastest  ||Yes| one directory's sub file names are stored in one key~value entry |
+| Cassandra    | O(logN)| unlimited | Local or Distributed, Very Fast||Yes|                |
+| MySql        | O(logN)| unlimited | Local or Distributed, Fast     |Atomic| | Easy to manage, export |
+| Postgres     | O(logN)| unlimited | Local or Distributed, Fast     |Atomic| | Easy to manage, export |
+| Etcd     | O(logN)| ~10GB | Distributed, 10,000 writes/sec     || | No SPOF. High Availability.|
+
+#### Switching between different Stores
+It is easy to switch between different filer stores.
+
+For example:
+```sh
+
+# first save current filer meta data
+
+$ weed shell
+> fs.cd   http://filerHost:filerPort/
+> fs.meta.save
+...
+total 65 directories, 292 files
+meta data for http://localhost:8888/ is saved to localhost-8888-20190417-005421.meta
+> exit
+
+# now switch to a new filer, and load the previously saved metadata
+$ weed shell
+> fs.meta.load localhost-8888-20190417-005421.meta
+...
+total 65 directories, 292 files
+localhost-8888-20190417-005421.meta is loaded to http://localhost:8888/
+
+```
+
+### Extending Storage Options
+
+For any new storage option, please implement the FilerStore interface. It should be fairly straight forward to implement. Welcome to contribute back.