[Dovecot] Highly Performance and Availability

Ed W lists at wildgooses.com
Mon Feb 22 14:36:36 EET 2010

On 19/02/2010 21:40, Wayne Thursby wrote:
> 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?

That's a LOT of IOPs for 16 disks to handle?  Given you are measuring on 
your existing hardware which has 5-10 disks depending on read/write 
(RAID10) then this surely means you are trying to push more than you 
state and just maxing out at the disk capacity?

I have no experience, but some reading over the last few days suggests 
you would very much desire an Equallogic with FC if the budget is 
there.  On the other hand buying two Dell/Supermicro machines with lots 
of disks and using DRBD to make each a duplicate of the other would 
appear to satisfy your requirements also? (perhaps cheaper, but less 
scalability).  DRBD sounds really nice for scalability up to a certain size?

Good luck

Ed W

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