Avamar f_cache2 size discrepancy between servers

Working with a customer on a performance issue and we ran across something that I am not sure is related, but did cause me to wonder.

The customer has 2x servers – one is their “active” file server at their primary location, and the second is a “alternate version” of the active server that is kept in sync via a product called “DoubleTake”. So at any given time, each server effectively has “the same amount” of data, files, directories, etc. on them.

At present, we are backing up the active file server to an Avamar/DD at the primary location – and we are also backing up the “alternate” file server to an Avamar/DD at the secondary location. FWIW, the performance issue we are seeing is that the “alternate” file server backs up “twice as fast” as the active file server does – or more accurately, since the amount of changed data is not actually that much, the “alternate” file server is “processing” the 20 million files that need to be backed up twice as fast as the active file server is. So we are looking at various aspects of what might be causing one server to scan through all those files faster than another.



Which brings me to the f_cache2 files – which I’m not sure have anything to do with this, but did look odd to me.



On the active file server, from what I can tell from the Avamar session logs and elsewhere, the f_cache2 file is just under 9GB, and there are around “980 pages in all backups in cache”.



On the alternate file server, from what I can tell from the Avamar session logs and elsewhere, the f_cache2 file is just under 47GB, and there are around “550 pages in all backups in cache”.



Can someone help me understand how one f_cache file is 5 times the size of another, but seems to contain only half the amount of “pages”, which as far as I understood were all the same size?

The only thing that I can think of is that we did have some issues in the past on the active file server that caused the Avamar cache files to be recreated a couple of times – so those files have not “been around” and been active for the same amount of backups that the cache files have on the alternate server (which as far as I know have not been recreated and have just been growing since the agent was installed on that server).

All comments/feedback appreciated – thanks.

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