[OpenAFS] Re: Is it possible to prevent caching local files?

Milan Zamazal pdm@zamazal.org
Sun, 03 Apr 2011 22:40:36 +0200

>>>>> "JA" == Jeffrey Altman <jaltman@secure-endpoints.com> writes:

    JA> Data stored in AFS volumes is location independent from the
    JA> perspective of the client.  The volumes are permitted to move
    JA> between servers while in use.  As such there is no concept of
    JA> local versus remote data.

Can a file server provide files other than from its own /vicep* mount
points?  If not then the client could handle data received from a file
server running on the same machine as "local" (at least at the given
moment and not assuming cases like when /vicep* is actually some sort of
a remote file system).

    JA> However, even if the cache manager could avoid caching data only
    JA> read from the local file server there would be a significant
    JA> overhead associated with the local reads compared to reading
    JA> from a local disk file system.

Yes, I've later found that in my configuration the hard-limiting factor
is the speed of the fileserver process.  But still copying data from the
local physical drive to another location of the same drive makes reading
from AFS about twice as slow than when using memory cache.

    JA> I would like to hear a better description of your use case.  Why
    JA> is there an AFS file server running on a client machine that is
    JA> a heavy consumer of data stored in AFS volumes on the file
    JA> server?  Perhaps AFS as it is implemented today is not the best
    JA> choice of a file system for your application.

I assume my use of AFS is not typical but it still makes sense.  I like
having all my home data stored in a single (virtual) storage, reasonably
robust, accessible and manageable from any local computer, with
authentication, access rights, caching (when it makes sense) and
replication (for basic backup and availability purposes).  I think AFS
serves this purpose better than NFS or Samba.  Convenience is generally
more important than performance, but sometimes, e.g. when doing
something with a photo collection or when processing a video, it's fine
when things run faster.