[Dovecot] Highly Performance and Availability

Stan Hoeppner stan at hardwarefreak.com
Sat Feb 20 01:39:23 EET 2010

Wayne Thursby put forth on 2/19/2010 3:40 PM:
> Thank you to everyone who has contributed to this thread, it has been
> very educational.
> Since my last post, I have had several meetings, including a conference
> with Dell storage specialists. I have also gathered some metrics to beat
> around.
> The EqualLogic units we are looking at are the baseline models, the
> PS4000E. We would get two of these with 16x1TB 7200RPM SATA drives and
> dual controllers for a total for 4xGbE ports dedicated to iSCSI traffic.
> I have sent the following information and questions to our Dell reps,
> but I figured I'd solicit opinions from the group.
> The two servers I'm worried about are our mail server (Postfix/Dovecot)
> and our database server (PostgreSQL). Our mail server regularly (several
> times an hour) hits 1 second spikes of 1400 IOPS in its current
> configuration. Our database server runs aroun 100-200 IOPS during quiet
> periods, and spikes up to 1200 IOPS randomly, but on average every 15
> minutes.
> With 4xGbE ports on the each EQL device, and also keeping in mind we'll
> have two of those, is it reasonable to expect 1400 IOPS bursts? What if
> both of these servers were on the same storage and required closer to
> 3000 IOPS?

The first thing you need to do Wayne is talk to your VMware rep and setup a
15-30 minute teleconference with a VMware engineer.  Or, if you have a local
VMware consultant/engineer, set a meet with him.  You need to get their thoughts
and recommendations on your goals and what you're currently looking at hardware
wise to implement them.

It sounds like you're set on using the ESX software iSCSI initiator, and using 2
to 4 standard GigE ports on each of your ESXi servers in some kind of ethernet
channel bonding and/or active/active multipathing setup.  I cannot say for
certain because I don't know the current certified configurations.  BUT, my
instinct based on prior experience and previous knowledge say this isn't
possible, and if possible, not desirable from a performance standpoint.  To do
this in a certified configuration, I'm guessing you at the very least will need
two single port iSCSI HBAs in each server, or one dual port iSCSI HBA in each

Please get the right technical answers to these questions from VMware before
shooting yourself in the foot, for your sake.  ;)

If it turns out you can't bond 2/4 Gbe iSCSI ports in an active/active setup,
you're probably going to need to go 10Gbe iSCSI, stepping up a few models in the
Equallogic lineup and stepping up to 10Gbe HBAs.  The other option (a better,
and cheaper one) is going 4Gb Fiber channel, as I previously mentioned.


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