[Dovecot] nfs director

[Charles Sprickman]

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
>