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Finding the Bottleneck

Hi all,

I was wondering if there is a way to find out what/where the bottleneck of
a large mail server is.

A client is running a huge mail server that we set up for them (running
qmail), but performance seems to be limited somewhere. Qmail has already
been optimized as far as it can go (big-todo patch, large concurrency
patch, etc.).

We're thinking one of the Hard Disks may be the main bottleneck (the mail
queue is already on a seperate disk on a seperate IDE channel from other
disks). Is there any way to find out how "utilized" the IDE channel/hard
disk is, or how hard it is going? Seems that right now the only way we
really know is by looking at the light on the server case (how technical
;-) ). Must be a better way...

The bottleneck wouldn't be bandwidth... it is definately with the server.
Perhaps the CPU or kernel is the bottleneck (load average: 4.84, 3.94,
3.88, going up to 5 or 6 during heavy mailing)? Is that normal for a large
mail server? We haven't run such a large mail server before (anywhere
between 500k to 1M per day so far, increasing each day), so ANY tips and
pointers would be greatly appreciated. We've already been playing around
with hdparm to see if we can tweak the disks, but doesn't seem to help
much. Maybe some cache settings we can fiddle with? Maybe the mail queue
disk could use a different file cache setting (each email being from 1K to
10K on average)?

Thanks in advance!


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