Explanation/Reference:

The most important thing to do on a client with so many files is to make sure that the file cache is sizedappropriately. The file cache is responsible for the vast majority (>90%) of the performance of thevamarclient. If there's a file cache miss, the client has to go and thrash your disk for a while chunking up a file thatmay already be on the server.

So how to tune the file cache size?

The file cache starts at 22MB in size and doubles in size each time it grows. Each file on a client will use 44bytes of space in the file cache (two SHA-1 hashes consuming 20 bytes each and 4 bytes of metadata). For 25million files, the client will generate just over 1GB of cache data.

http://jslabonte.blogspot.com/2013/08/avamar-and-large-dataset-with-multiples.html