[Dovecot] FreeBSD, Dovecot and ZFS

[Ben Morrow]

At  9PM +0000 on 12/02/13 you (Jason Lock) wrote:
> Mail Issues - FreeBSD
> 
> Hello, my apologies if this may be the wrong forum but hoping that
> maybe someone might be able to provide some insight.

This may turn out to be something better addressed on freebsd-stable,
but this is a perfectly good place to start.

> Have a very sporadic and strange issue with our mail servers running
> Dovecot on FreeBSD.  There are three servers hosting Dovecot with
> FreeBSD as the underlying operating system.  All three connect to a
> NAS server, again running FreeBSD and ZFS.

Over NFS, I assume? What version, what mount options, and what type of
authentication? What locking strategies is Dovecot using? Are there any
suspicious messages in syslog on either machine?

> When the specific issue occurs, clients connecting to check mail via
> POP3 or IMAP experience long delays and timeouts.  To the point where
> POP3 Logins fail due to the timeouts.  The issue is further compounded
> by clients increasing the number of attempts to check mail.

Are the delays happening before or after login?

If you can provoke this and get a 'procstat -k' for the relevant dovecot
process this might be helpful. If 'long' delays means several minutes,
running something along the lines of 'procstat -k $(pgrep -U dovecot -U
doveauth)' every minute or so for a while might be one way to catch
this, though this will collect a lot of data rather fast so you will
need some way to locate the relevant entry.

Ben