[Dovecot] IMAP

[Rick Romero]

  Quoting Jason Lock <JLock at csolve.net>:

> We are using version 1.2.17 and recently are experiencing major issues
> with performance, which we believe have isolated to IMAP sessions.
>
> We have 3 servers running Dovecot, with a central store shared via NFS. 
> Things have been running quite well for months now, with the latest
> issues appearing within the last week.
>
> As an experiment have 2 of the server running and only accepting POP3
> connecitons no IMAP, and the 3rd server only accepting IMAP connections
> and no POP3.
>
> When the issue occurred today, stopping dovecot on the IMAP only server
> allowed POP3 to resume to normal operations 5-10 minutes later.  Leaving
> IMAP disabled for a period of time (about 30 mins) and then re-enabling
> seemed to worked the first time.  Subsequent times, the issue appeared
> shortly after re-enabling IMAP.
>
> Our webmail solution connects via IMAP, so when disabled this also
> impact clients using the webmail.
>
> Running only POP3 while IMAP is disabled we do not appear to have any
> issues.
>
> At this point, looking for any advice.  We believe the number of devices
> utilizing IMAP has increased significantly for us, and whether or not a
> specific device is the cause we have not been able to determine.
> Anyone else experiencing a similar problem that appears related to IMAP?

I'd suggest checking your I/O load on the NFS server.    Especially If
you have a need for that many front-end machines, that's the first place
I'd check.  I'm not sure if Dovecot 1.x support it offhand, but moving the
indexes to a local SSD on the IMAP only server might help if it's an I/O
issue..
You could also try running IMAP on the NFS server - assuming it's capable.

Personally, I had a hell of a time with certain versions of FreeBSD as an
NFS Client. In my case the server that acted up was an SMTP server for
incoming delivery only. For whatever reason, it would cause EXTREMELY slow
access on the NFS host and drag everything down.   This happened to me
with both FreeBSD and OpenSolaris as the NFS host. I have no idea why, but
an upgrade/rebuild fixed my issues. This probably isn't your issue, my
problems cropped up almost immediately, but it's something to keep in
mind.  Check your load on the NFS server first.

Rick