Re: [exim] Speeding Up Exim

Am Samstag, den 01.03.2008, 12:48 -0600 schrieb Matt:
[...]
> Hardware is:
> AMD64 Dualcore 3800+ just updated to 5600+
> 4Gbyte DDR2
> SATA2 500GB drive
>
> Normally load average is like 8 or less but at peak times I am seeing
> it spike to like 100 area. Upgrading the CPU gained very little. I
> am thinking I am disk I/O bottle necked. I have about 2000 email
> accounts and according to eximstats at peak times I am seeing
> "Messages received per hour" of 40K.
Actually, so far you failed to state a problem.
Load is something like "number of processes waiting to be processed" and
I have seen servers with load-values higher thann 1000 which still
reacted faster than my laptop.

Load is not a problem. It might indicate a problem, but load itself is
only a symptom.

Disk-IO might be an explanation for "high" load-values. There are
countless others. Find the real one before desperatly trying out
possible solutions... when I read your questions and the first answers
which all circled around "optimising disk-io by tuning the kernel" I
just felt desperation. Nobody even considered wheater or not your
asumptions sound reasonable. Nobody even asked questions....

First, 2000 email-accounts does not sound like a big deal, the number of
messages does. But of course, that's just 20 messages/mailbox. You
mention one harddisk and that you can't afford a long downtime. That
worries me. You can't provide reliable service without decent storage
(raid 1 or raid5, and backup, of course) and regular maintenance. Fix
that.

In order to understand the real problem, you need data about your
system. For example, recent top (I prefer atop) with recent kernel will
show a value "wa" which is short for waiting. If you really have a
problem regarding disk-io, "wa" should show this.
Cpu(s): 1.4%us, 0.5%sy, 0.0%ni, 98.1%id, 0.0%wa, 0.0%hi, 0.0%si,
0.0%st

I highly recommend running "munin" on every exim-server. It will gather
lots of numbers regarding your server, which can be invaluable when
facing problems.

In my experience the most likely cause for high load-values on
exim-serves is DNS-related. If you process 40k messages an hour and use
SpamAssassin, more than 500k DNS-requests are likely. If you didn't
worry about a local caching-DNS-daemon on your mailserver, than you
should do that now. If you already have a local caching-DNS-daemon on
your mailserver, consider moving it to a different server.

Any further advice would be wild guessing, so it's up to you to provide
further data.

--
CU,
Patrick.