[Dovecot] rc14 and rc15 performance issues

Ethan Sommer sommere at gac.edu
Tue Nov 21 02:05:37 UTC 2006

Curtis Maloney wrote:
> Jeff A. Earickson wrote:
>> Our IMAP server is seriously underpowered and needs to be replaced.
> Just out of curiosity, how many users are we talking here?

Colby appears to have 1,871 students, about 220 faculty and I'm guessing 
250 administrators/staff. So 2340 or so.

I sympathize with your situation, I've been there. We have "Chapel" for 
a half hour every day, and _maybe_ 5% of our students/users/staff go to 
chapel, so (and we have closer to 3000 users) we have at least 2x our 
peek usage not counting chapel during that time.

(and before I say this, I understand that your immediate problem is 
possibly a difference between rc13 and rc14/15 but I thought you might 
appreciate the knowledge of what we did in essentially the same 
situation as I imagine that even if the problem is solved this week by 
finding a memory leak its only a matter of time.)

We used to run UW IMAP on Solaris using mbox. When we did we did a few 
things which did a good job of acting as stopgates:
1. We moved from using raid5 to raid 10. Based on some benchmarks I did 
recently on modern hardware which will soon be one of our dovecot 
cluster machines, raid 10 is about 3x as fast for block writes and 50% 
faster for block reads than raid 5.
2. We added more ram. Which, if you are possibly swapping you should 
certainly do, but even if you aren't the more ram you have the less 
often you have to touch the disks due to cache.
3. We added a 3rd mirror to our raid 10.

(then we moved to a linux box with 6g of ram and 22 1k fc disks for 
inboxes in raid 10 running uw imap)

Hmm, perhaps people would like to see the results of the benchmarks I 
ran on this list...

Ethan Sommer

Ethan Sommer
Systems Administrator
Gustavus Adolphus College
sommere at gac.edu

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