[Dovecot] RAID benchmarks (fixed results.. oops)

Ethan Sommer sommere at gac.edu
Tue Nov 21 02:46:49 UTC 2006

not sure how I messed that up so badly, the first set of  numbers were 
off. here's the first numbers again:
      Output                   Input
RAID  "Per Chr" "Block" "Per Chr" "Block"
RAID6  38918,    60365,  40098,   301104
RAID5  38689,    64907,  40320,   282653
RAID10 38816,   229062,  40645,  267418

All numbers are KByes/second. So the raid 6 can do block reads at about 
300megabytes per second (for one thread) and the 4 threaded raid10 
bellow did 230megabytes per second with 4 threads.

Too many numbers in too big a spreadsheet I guess. In any case, that's 
what I actually got.

Ethan Sommer wrote:
> We (a small college with about 3000 active accounts) are currently in 
> the process of moving from UW IMAP running on linux to dovecot running 
> on a cluster of 3 or 4 new faster Linux machines. (Initially using 
> perdition to split the load.)
> As we are building and designing the system, I'm attempting to take 
> (or find) benchmarks everywhere I can in order to make informed 
> decisions and so that when we need something faster we have something 
> to compare it to. I've looked all over the Internet and I haven't seen 
> very many good benchmarks running on recent hardware for things like 
> this. Even simple things like how different raid levels perform with 
> fast CPUs and really fast disks.
> We recently got the first of the cluster machines (which has the 
> following specs: (from penguin computing)
> 2x 1.6ghz woodcrest (so 4 cores total)
> 2g ram (we may upgrade to more, depending on what we seem to need)
> 6x 15k SAS 73G hard drives.
> I've always read that RAID 10 is the RAID of choice for mail, because 
> the checksums take time and whatnot, but on a system that fast I'm 
> sure that's not an issue (which I could see from the cpu usage during 
> benchmarks.) We were also wondering whether RAID6 would be a good 
> option since it would give more redundancy. (raid6 allows 2 drive 
> failures)
> All tests were run on ext3 with all 6 disks in the raid. Everything is 
> using Linux software raid.
> I used bonnie++ to run the benchmarks, and here are the initial 
> results we got:
>       Output                   Input
> RAID  "Per Chr" "Block" "Per Chr" "Block"
> RAID6  34628,    97983,  23316,   39077
> RAID5  39559,    32715,  32036,   52231
> RAID10 38816,   229062,  40645,  267418
> I assume that mail running maildir (as we intend to do) is somewhere 
> between writing one char at a time and writing huge blocks to fill 4g 
> files. Since the Per Chr values seemed to have maxed out the CPU and 
> we'll have 4 cores available, I tried the same thing running 4 copies 
> of bonnie at once and adding the results. (I worked backwards and 
> didn't bother with raid 6 for obvious reasons)
>       Output                   Input
> RAID    "Per Chr" "Block" "Per Chr" "Block"
> RAID5   37465,    37095,  102828,   174263
> RAID10 111239,   128287,   93400,   230320
> So, if our system is ever running full out, basically disk bound, it 
> should be able to handle about 4X as many writes and at least as many 
> reads using RAID10 than raid 5, and since raid 6 was pretty similar to 
> raid 5 in the first tests, I assume it will be here too.
> I have the full bonnie results if anyone's interested.
> I also plan to come up with some basic benchmarks as we start to 
> actually have dovecot working as we want it to. (Possibly using the 
> macs in our labs and XGrid as a "client".. finally a use for that 
> thing :) )
> Do people have suggestions as to what to test for a primarily IMAP (+ 
> a little POP) server? I was thinking of doing something similar to 
> http://www.courier-mta.org/mbox-vs-maildir/ which selects a mail box, 
> deletes and expunges a message, fetches a few messages, and then does 
> some searches.
> Also, while I have the opportunity, are there any other benchmarks I 
> should run? I suppose I could compare dovecot with mbox vs maildir, 
> with indexing and without. Dovecot with indexing but the indexes 
> deleted, etc. I could compare dovecot to uw imap.
> Anything else? I probably can't justify the time to get cyrus up and 
> running. (I did that a few months ago when deciding which server to 
> use...)
> Ethan Sommer

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

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