[Dovecot] RAID benchmarks

[Joseba Torre]

Hi,

we have over 6000 active accounts (half pop3, half imap), and switching 
from UW+mbox to dovecot+maildir was such an incredible performance 
boost that the same old hardware was more than enough. Also from our 
experience, disk I/O was critical with mbox, but not now (we keep using 
raid5 without performance penalties). Test it before you switch.

Aaaaaaaaaaagur.

El Martes, 21 de Noviembre de 2006 03:37, Ethan Sommer escribió:
> 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

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