[OpenAFS] Speed tests on our AFS Cell

[Esther Filderman]

On 4/13/05, Matt Elliott <melliott@ncsa.uiuc.edu> wrote:
>=20
> On Apr 13, 2005, at 6:53 AM, Lars Schimmer wrote:
> > Another question I've got is about cache-size:
> > I read somewhere to set cache size to roughly 1 GB on disk cache. Is
> > it a real
> > nice one to set such a big cache at normal work or is it more like a
> > showstopper
> > and 50-100 MB Cache is better?
>=20
> My experience is that you want your client cache to be at least as
> large as the largest files you are using.  Performance on files that
> won't fit entirely in the cache is terrible.  I use a 2GB cache on my
> system since my fileservers currently have a 2GB file size limit.

Setting cache size is a bit of a black art.  You *really* need to take
into account what your machine is doing and how many users are on it.=20
A machine that's generally used for reading email for lots of users is
not going to have the same requirement as a machine that does
calculations of huge datasets.

If you have a machine that is mostly used for lots of small files and
you give it a 2G file limit because "someone is using 2G files there
for some other project" you are mostly going to be very sad.  The
cache design will make hunting through a 2G cache for tiny files to
expire is going to slow things down considerably.

Remember also: the speed of the cache is slow because of the way it is
structured, but the good side of the way it's done is that there's a
lot of safety and sanity checking to make sure that both the users
don't get crap and that garbage isn't written  back to the
fileservers.