[OpenAFS] Some AFS Architectural Questions

Christopher D. Clausen cclausen@acm.org
Fri, 27 Oct 2006 17:52:05 -0500

Daniel Clark <dclark@pobox.com> wrote:
> On 10/27/06, Leggett, Jeff <jeffrey.leggett@etrade.com> wrote:
>> How does AFS compare to its stateless communication with NFS?  We
>> have had problems with vendors using NFS to maintain links (EMC
>> comes to mind) to storage arrays, that fail often and hard.
> I'm not quite sure what you mean by "using NFS to maintain links", but
> in any case AFS (like NFSv4 and CIFS) maintains state; is practice the
> behavior is roughly analogous to hard NFS mounts (i.e. client blocks
> until the server comes back).

One of the reasons we moved to AFS from NFS is because we would need to 
completely reboot machines if NFS ever became wedged.  (Well, that and 
better Windows support.)  AFS has always recovered from accidental 
server reboots (don't name your servers afs1, afs2, afs3, its too easy 
to reboot the wrong one by typo :-) and forced restarts of the fs 
instance for whatever reason.  Sometimes the machine needs to be helped 
out a little with an fs checks and fs checkv command, but a reboot has 
not been required to date.

> However for read-only volumes with copies on multiple servers, if one
> server goes down, the client automatically fails over to another
> server.

Yes, this is quite useful.  You can also use the RW volume as staging 
area and then vos release out to the RO volumes once tests have been 
done.  We use it for our main website, keeping a copy on every server in 
case one goes down our website should stay up.  I assume that you have 
much more data with more importance than the web pages for a student 

If you want to keep multiple seperate environments, you can trivially 
copy volumes (vos copy,) or dump (vos dump) and restore (vos restore) 
them to different ones.  Should be significantly easier to maintain 
long-term than NFS.  Dumps can even be moved between seperate AFS cells, 
with certain caveats.

Christopher D. Clausen