[Dovecot] Dovecot + DRBD/GFS mailstore

[Eric Jon Rostetter]

To update an old thread...

>> I'm looking at the possibility of running a pair of servers with
>> Dovecot LDA/imap/pop3 using internal drives with DRBD and GFS (or
>> other clustered FS) for the mail storage and ext3 for the root drive.

> I'm in testing right now with this setup.  Two Dell PE 2900 servers
> (quad core @ 2.3 GHz, 8 GB RAM, raid 10 for the GFS+DRBD disk, raid 1
> for the ext3 disks).  Running DRBD as a master/master setup.
[...]
> So far it is early testing.  63 users, but only about 12 of those are
> "power users".  The performance has been real good so far, but as I say,
> not many users yet.

Well, as of yesterday, I've gone "live" with this setup with about 1K users.
Averaging about 150 to 200 concurrent sessions (higher during certain
day hours, lower at night, etc).

Slightly slower with 1K users than with 63 users (of course) but so
far it is proving very stable and reasonably fast.

Most of the time it is performing faster than my old system with similar load,
though there are rare "stalls" of webmail imap operations (connect, get data,
and disconnect session) where it might take about 5 to 10 seconds to complete.
I'm thinking it is a locking issue, but not sure.  The average time for such
a webmail operation is 0 to 2 seconds (which is reasonable, based on the
message/mailbox size; using mbox here, so we have some 2 GB to 3 GB mbox
files with large messages in them, etc).

Anyway, the point is that doing a cluster like this is very reasonable
from a cluster/stability point of view.  Jury is still out on performance,
but I should know soon since I've now got a "significant" number of users
hitting it.

My gut feeling is that there will be some slow connections from time to
time due to locking probably, but that overall it will scale under load
better and not die when a spammer attacks us or we otherwise get flooded...

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

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