[Dovecot] Highly Performance and Availability

Wayne Thursby wayne.thursby at pgllc.com
Tue Feb 16 07:42:57 EET 2010

Hello everyone,
   I am currently running Dovecot as a high performance solution to a particular 
kind of problem. My userbase is small, but it murders email servers. The volume 
is moderate, but message retention requirements are stringent, to put it nicely.

Many users receive a high volume of email traffic, but want to keep every 
message, and *search* them. This produces mail accounts up to 14+GiB. After 
seeing the failures of my predecessors, I transitioned to Postfix/Dovecot and 
haven't looked back. Things are running nicely with the below setup.

Postfix and Dovecot running on the same virtual machine on a Dell 2950
with 1x Xeon E5440 on ESXi 4. Maildirs served up by 10x146GB 15k RPM SAS drives 
on RAID-10 via direct attached Dell MD-1000.

We are transitioning other services to high availability, and I'm wondering 
exactly how to provide some kind of near-realtime failover for my 
Postfix/Dovecot machine. The MD-1000 provides nothing in the way of iSCSI, but 
it *does* have two SAS connections available, only one of which is in use.

I have been looking at the Dell EqualLogic stuff and it seems to provide what we 
need. I can get most of the information I need from the rep, but I wonder if 
anyone has any experience with high performance requirements on these kinds of 

I'd like to continue running my current hardware as the primary mail server, but 
provide some kind of failover using the SAN. The primary usage of the SAN will 
be to make our 2TB document store highly available. I'm wondering what kind of 
options I might have in the way of piggybacking some email failover on this kind 
of hardware without sacrificing the performance I'm currently enjoying.

Is it possible to go with a virtual machine mounted on iSCSI acting as a backup 
mail server? How would I sync the two, NBD+MD? Any experience doing this with 
maildirs? I wonder about the performance.

Can it be as simple as attaching my MD-1000's second controller to the SAN magic 
box via SAS and pressing the Easy button?

Is it as expensive as running my primary mailserver mounted from the SAN via 
Fiber Channel? Will that get me under 30ms latency?

I welcome any suggestions the group may have.

Wayne Thursby
System Administrator
Physicians Group, LLC

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