Avamar client files f_cache.dat and p_cache.dat

At the beginning of a backup, the Avamar client process, avtar, loads two cache files from
the var directory into RAM

•  f_cache.dat (a.k.a "File Cache")

• p_cache.dat (a.k.a "Hash Cache")

The f_cache.dat cache file 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 p_cache.dat 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. The hash cache is
very important when backing up databases.

By default, the maximum File Cache size can be 1/8 of the RAM and the maximum Hash Cache size will 1/16 of the RAM.

Because the avtar program is a 32-bit application, the maximum file cache size that avtar
can use is limited to less than 2 GB. In an example where a client has 4 GB of RAM, the
maximum size of the file cache is 352 MB.
Each entry in a file cache comprises a 4-byte header plus two 20-byte SHA-1 hashes (44
bytes total):

• SHA-1 hash entry of the file attributes. The file attributes include: file name, file path, modification time, file size, owner,group, and permissions.

•  SHA-1 hash entry for the hash of the actual file content, independent of the file attributes.