Coda File System

Re: FAQ: Is Coda ready for use?

From: Stephen J. Turnbull <>
Date: Mon, 01 Dec 2003 11:09:52 +0900
>>>>> "Lionix" == Lionix  <> writes:

    >> We plan to use coda on the whole faculty to provide user home
    >> dirs and data. This would be nearly 200 machines and 1000
    >> users. Is coda ready for such a usage or would we run in
    >> trouble?

    Lionix> Wow ! I've seen a 30 machines configuration stuff in the
    Lionix> ml two years ago but i've never heard about so big
    Lionix> deployement of coda-fs.  Guess you'll have to define
    Lionix> multiple realms.

I don't see why.  Maybe multiple servers, multiple VSGs for
performance or organizational reasons, but Coda scales well in that

    >> Is it possible to deactivate the cache on the client machines
    >> at runtime?

    Lionix> I would say no.. caching mecanism is a full part of the
    Lionix> coda client ( venus ).

"No" is right.  The way the client works is to fetch whole files into
the cache (thus performance of open() on very large files is poor),
and access them from there.

RVM (where the directory structure is kept) can be disabled when
initializing the client, but this means you need to keep all
information in memory, and of course it's not persistent.  Increases
startup costs and risk of mutation loss if there's a crash before

    >> Does coda need a process in userspace to access the coda fs?

    Lionix> If you mean a process started by the user the reponse is
    Lionix> no.  Coda must be started by the root, init script stuff.

Ie, "yes".  The coda client is quite complex; the kernel provides only
enough services to implement to VFS interface, so that ordinary
programs can use usual file APIs.  All real work is done by upcalls
into the client (which is actually a server from the point of view of
other processes accessing it:

Unix process <-+  +--> venus daemon <---------> coda server
               |  |          A
           VFS |  | Coda     |
      downcall |  | upcall   |
               |  |          |
               V  V          V
              kernel     file cache

and any file data returned follows the opposite path.

Institute of Policy and Planning Sciences
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Received on 2003-11-30 21:16:21