[OpenAFS] Re: Maximum disk cache size

Joe Buehler jbuehler@spirentcom.com
Mon, 31 Oct 2005 09:18:31 -0500

chas williams - CONTRACTOR wrote:

> there have been some discussions on the openafs-devel list recently about
> cache tuning.  check the archives.  the 1.4.x branch also has the "new"
> default cache tuning (auto chunksize selection and different assumption
> for average file size).
> if you gave us a little more information some others might be able
> to make some educated guesses.

OK, I did some reading and think I understand what is going on.

There appear to be 3 main parameters:

- cache size (cacheinfo file)
- chunk size (afsd argument -chunksize)
- number of cache files (afsd argument -files)

Default behavior is for afsd to use a chunk size of 64k and to
calculate the number of cache files based on the cache size and
an assumption of average cached file size of about 10k.

A large cache results in a large number of cache files, which
may not be desirable because of the kernel memory required
to support this.  So it is best to cut down the number of
cache files -- the assumption being that your average file size
is larger than 10k, of course...
Joe Buehler