[Dovecot] Dovecot and SSD

Brett Dikeman brett.dikeman at gmail.com
Fri Jul 30 07:14:41 EEST 2010

On Thu, Jul 29, 2010 at 9:05 PM, Curtis Maloney <cmaloney at umd.com.au> wrote:

> Umm... apart from "shiney toys", is there any legitemate reason for such
> expense on performance tuning?

SSDs are a perfectly legitimate technology for a mail server which
deals with a lot of random IO.  Hell, they're a perfectly legitimate
application of technology for most server environments if you can deal
with the storage density, and size them appropriately.  They're more
reliable, use less power, and in PCI-E form are shockingly fast.

In fact, I'd go so far as to say that SSDs should be seeing much wider
adoption in IT.  Most people are far too scared about the write cycles
in particular...as long as you don't fill the drive completely full
and your OS supports TRIM, most SSD's will outlast the machine they're
put into.  We've got a Solaris box with a fairly small (32GB, I
think?) Intel SSD in it for its OS; it's mostly empty (the meat and
potatoes are the 4x2TB drives used for data storage) and I expect the
drive will never die.

> I ask because we have about 30 users using our IMAP server (Dovecot 1.1),
> which also serves as our main Samba server, and until recently was also a
> CUPS server.

30 users?  I've got almost ten times that- as I'm sure many other
admins here do and I'm on the low end of the scale in terms of # of
users. Our mail spool sits on 4x 10k RPM U320 drives in RAID10, and
iowait values that climb up towards ~15% sometimes.  As we look at
replacing the system, we're strongly eying an SSD because it'll be a
huge jump in performance.  An SSD will also help with cutting power;
I'm hoping we'll end up using half as much power.  It'll also be more
reliable, though we've dropped only one drive in the course of 5-6
years in this particular machine.

> This on a Sun V100 ( 450MHz UltraSPARC-IIi ) with 1G RAM and two dull,
> standard IDE HDDs ( a 40GB for OS and mail, and a 320GB for Samba).

You're not using redundant storage (is there a particular reason why?
Mailspools are far too important and dynamic to trust to just nightly
tape), you've got a less-than-40GB mailspool, and "1 user" is not a
standardized unit.  I'm guessing your server is also sitting behind
something between a T1 and a sDSL line?  Or that such a line sits
between your server and your users?

  I have half a dozen users who have more email than your entire
mailspool.  Our total mailspool is creeping past half a terabyte.  We
run mailing lists with hundreds of local and remote users on them that
generate big spikes in load, and we do spam processing (even with
spamd, spamassassin is a hog.)


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