[Dovecot] RAID benchmarks

Joseba Torre joseba.torre at ehu.es
Tue Nov 21 07:34:41 UTC 2006


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.


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

Trying to make bits uncopyable is like trying to make water not wet. 
The sooner people accept this, and build business models that take 
this into account, the sooner people will start making money again. 
        - Bruce Schneier

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