Coda File System

Re: Considering CODA

From: Jan Harkes <>
Date: Thu, 12 Jun 2003 13:36:42 -0400
On Thu, Jun 12, 2003 at 10:54:26AM -0400, Doug Eubanks wrote:
> I need a shared storage solution for a RedHat Advanced Server cluster that I
> would like to build.  The server will perform clustering of several
> services....including web, DNS, and the biggy...mail (using sendmail and
> procmail and qpopper).  I do not want to use NFS for the obvious reasons
> including the lack of file locking.  Is CODA suitable for sharing
> filesystems that have a lot of constant read/writes from different clients
> (such as a mail spool)?  What would the performance hit on the servers and
> clients be?  Can you have two or more CODA servers maintaining a complete
> copy of the filesystem?

Coda does not provide file locking either. To deal with maildelivery
you would need to use maildir, which is in fact also the solution you
would use to reliably deliver mail over NFS.

I can guess for the other obvious reasons,

- replication
    Coda is a unique as we use optimistic strategies, we try to allow
    read/write operation even if we cannot reasonably guarantee that the
    operation will in fact succeed. When, as a result of this optimism,
    we end up with conflicting updates and cannot fix it up with simple
    heuristics, the problem is punted to the user. Great for research,
    but difficult for 24/7 operation with no supervision or non-expert

- file caching,
    Again our optimism allows for great flexibility, because you can
    still have read/write access to cached files and directories even
    when all the servers are unavailable. And again, any problems are
    punted to the user.

    AFS also provides caching, has file-locking and will tranfer large
    files in smaller chunks. Ofcourse it has read-only replication and
    read-only access to cached objects while disconnected from the

    Solaris has cachefs to provide caching for NFS. I don't know whether
    there are FreeBSD or NetBSD implementations for this, but Linux
    definitely doesn't have it yet.

On the other hand, people are doing pretty much the things you mention.
Our www.coda webpages are all being served from Coda, my email is
automatically delivered to my homedirectory in /coda, and other people
outside of CMU have been doing similar things.

So it isn't necessarily a bad idea, it just depends on your situation.

Received on 2003-06-12 13:39:56