On Sat, 28 Aug 2010, Cor Bosman wrote:
We might be a slightly larger install than you (60k users, mail on FAS 3170
Metrocluster), but we have noticed corruption issues and the director is
definitely going to see use in our shop. We still use Sendmail+procmail for
delivery, so no issue there... but we've got hordes of IMAP users that will
leave a client running at home, at their desk, on their phone, and then will
use Webmail on their laptop.
Without the director, all of these sessions end up on different backend
mailservers, and it's basically a crapshoot which Dovecot instance notices a
new message first. NFS locking being what it is, odds are an index will get
corrupted sooner or later, and when this happens the user's mail
'disappears' until Dovecot can reindex it. The users inevitably freak out
and call the helpdesk, who tells them to close and reopen their mail client.
Maybe you're small enough to not run into problems, or maybe your users just
have lower expectations or a higher pain threshold than ours. Either way,
it's unpleasant for everyone involved, and quite easy to solve with the
director proxy.
We are in the exact same position as Brad. We also use sendmail's LDA, we
also use a metrocluster, and we also have hordes of imap and webmail users.
We see the exact same thing Brad sees. And I see it myself about once a week
as well. The index gets corrupted due to access by 2 different clients, and
to the user it then looks like their mail disappears. The user totally freaks
out, because they'll invariably have really really important mail that has
to be recovered right now. Usually a law firm as well. They call the helpdesk,
keeping a support person busy with something thats really just a known bug.
It probably isnt much of an issue if you use POP. But in large scale IMAP
setups, where people are getting used to having access to all their email
server-side (and thus mailboxes growing, needing larger indexes, increasing the
chances of problems) from a myriad of clients this WILL happen if you're
using NFS.
Ive even considered moving away from NFS again for indexes due to this
problem. But it really is noticable if you have a lot of email that your
index isnt up to date as you move across our dozens and dozens of imap
servers.
Any idea how Rackspace has implemented the director? They have to be
using some kind of shared storage, it wouldn't make sense to make storage
local to each host in such a large environment.
Charles
Cor
