[Dovecot] So, what about clustering and load balancing?

[Eric Rostetter]

>> On 14.2.2010, at 3.31, Stan Hoeppner wrote:
>>
>> I can't see how the metadata sharing of say GFS2 is going to create  
>> any serious
>> performance impact on a cluster of dovecot servers using GFS2 and a  
>> shared SAN
>> array especially if using maildir.

While I use GFS shared on a cluster with dovecot for mbox and think the
performance rocks, this really depends on the setup (mbox may be worse
than maildir, how much hardware you have for it, how you load balance, etc)
and what you consider good/bad performance (what is fast to me might be
slow to you) as well as of course scale (might work for 2K users, but what
about for 200K or 1.5M).

>> If the load balancing is implemented
>> correctly and a given user is only hitting one dovecot server at  
>> any one point
>> in time, there should be few, if any, shared file locks.  Thus, no negative
>> impact due to shared locking.

This ignores the delivery of mail to the user (again, not so bad for maildir
but a killer for mbox).  If the delivery is on a separate box than dovecot
your can have lock contention...

Also there may be other things to cause lock contention like backups,
admin cron jobs to check things, etc.

Anyway, I run dovecot in a cluster without any issue, but that is because
of my client base and performance expectations (and some real nice hardware).

-- 
Eric Rostetter
The Department of Physics
The University of Texas at Austin

Go Longhorns!