[OpenAFS-devel] tweaking openafs configuration - chunksize, cache expiration and cache renewal

[Stephan Zimmer]

Hi guys,
this is my very first post to this mailing list and I hope that someone
following the list could point me to a solution for this bunch of
questions I am going to ask in this email.

We are trying to utilize AFS in order to avoid the installation of local
software on our machine by sourcing precompiled versions from a
different cell. As the cell we are fetching our data from is located
1000 km away from us we are experiencing serious latency issues although
our cache of currently 50 GB should give us plenty opportunities to
cache whatever we need.

Tests showed in fact that sub sequential exercising of the same tasks is
not as performant as we would have expected it: after having run it for
the first time I would have thought that the second call (from a
different user though) should entirely rely on the cached content the
first user had created during his call. However, it appears as the cache
content expires very soon after having accessed it for the first time.

For our particular setup we were thinking of setting up our machine to
cache entire parts of the cell we were taking our stuff from and do this
caching via a cron job. This apparent expiration appears to be a major
drawback but after having read a bunch of references I couldn't figure
out what to change in our configuration.

The other issues is whether it is advised to change the chunksize as
this would reduce the chunks that are used for a generic file transfer.
Is it recommended to change this parameter - does it bring much
performance?

Lastly, how do you guys think about the general plan - setting up an
afs-configuration that caches entire afs volumes from a designated cell
once a day or something... is this really practically or rather not
recommended due to performance issues?

Any help would be highly valued,
thank you very much,
cheers,
Stephan Zimmer


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Stephan Zimmer
Uppsala Universitet
Department for Physics and Astronomy, Nuclear- and Particle Physics