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Re: Solid State Hard Drives

On Thu, Oct 08, 2009 at 12:53:15PM +1100, Glenn Hocking wrote:
> Running sendmail, qpopper, roundcube webmail, dspam, clamav-milter on
> a HP DL360 G4 with 5000 accounts and it is struggling, time for an
> upgrade and looking at all options.

there's your problem. switch to postfix and watch your mail queue load
problems vanish instantly. i've done this numerous times over the years
on sendmail boxes that are struggling to keep up with the load - postfix
on the exact same hardware, with the exact same mail load copes without
even breaking a sweat.

also recommended: use some carefully selected RBLs such as
zen.spamhaus.org[1], as well as grey-listing. these will reject the
majority of spam before it gets to dspam/clamav and your mail queue,
greatly reducing both CPU and I/O load.

another recommendation: add more memory. as much as will fit into the
machine. memory is cheap[2] and is STILL the single most effective thing
you can do to improve the performance of any disk-I/O bound system like
a mail server.  With enough RAM to buffer the disks, many emails will
never touch the disk at all - queued, sent/delivered, or rejected and
then deleted entirely from RAM.

BTW, 5000 user accounts isn't a lot, certainly not for a DL360....but
it isn't the number of users that matter, it's the amount of mail the
server sends and receives...which has a lot more to do with spammers
(who will routinely spam thousands of non-existant addresses at your
domains) than it has to do with your users.

> Solid State drives are not too expensive these days, actually
> comparable to fast SAS drives with high end RAID controller.

and for the kind of usage pattern seen on mail servers, they'll slow
down to a crawl within weeks if not days. 

rather than a flash SSD, you're probably better off putting the mail
queue drive on a RAM disk...not a software RAM disk (unless you're
a gambler), but a battery-backed hardware RAM disk like the ACARD
ANS-9010[3].  you probably wouldn't need more than 1 or 2 GB for
the mail queue.

these ACARD devices can take up to 64GB of DDR2-800 RAM (8 x 8GB
sticks), so depending on how much mail your 5000 users receive (and
store long-term) on your server it might even be possible to place the
mail spool (e.g. /var/mail and/or user Maildir directories) on the

[1] http://www.spamhaus.org/zen/

[2] 1GB & 2GB memory sticks are dirt cheap.  4GB sticks are just
starting to become reasonably priced.  8GB sticks are still rare and

[3] http://techreport.com/articles.x/16255


craig sanders <cas@taz.net.au>

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