You can find those very well described in best practice guide.

In short and raw, file cache is mostly used for backup of file system data while hash cache will be used for block level thingy like databases. They are used whenever you do backup. These databases are on client and they get loaded into memory every time service/daemon starts. They have their default values which you may change based on sizing you did for server you backup. I would recommend to read best practice guide which gives some very good example of those.

These parameters are used to basically identifying what have been backed up previously and hence will:

1. Reduce the amount of time required to perform a backup
2. Reduce the load on the Avamar client
3. Reduce the load on the Avamar server


The file cache stores a 20-byte SHA-1 hash of the file attributes, and is used to quickly identify which files have previously been backed up to the Avamar server.

The hash cache stores the hashes of the chunks and composites that have been sent to the Avamar server.The hash cache is used to quickly identify which chunks or composites have previously been backed up to the Avamar server

At the beginning of the backup, the avtar process loads into memory two cache
files from the var directory (this directory is found in the Avamar installation
path). So these files exist in var directory i.e. in Avamar installation path but are loaded in memory when backup begins.

Thanks and Regards,

Randeep singh