diff --git a/Optimization.md b/Optimization.md
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 Here are the strategies or best ways to optimize SeaweedFS.
 
+## Use LevelDB
+When starting volume server, you can specify the index type. By default it is using memory. This is fast when volume server is started, but the start up time can be long in order to be loaded file indexes into memory.
+
+`weed volume -index=leveldb` can change to leveldb. It is much faster to start up a volume server, at the cost of a little bit slower when accessing the files. Compared to network speed, the extra cost is not that much in most cases.
+
 ## Preallocate volume file disk spaces
 
 In some Linux file system, e.g., XFS, ext4, Btrfs, etc, SeaweedFS can optionally allocate disk space for the volume files. This ensures file data is on contiguous blocks, which can improve performance when files are large and may cover multiple extents.