Load spikes when new email arrives

[francis picabia]

Here are more stats.  Do these look average for performance?
It is difficult to understand why the system was working with few
load spikes before.

A mailman mailing list sends 10kbyte message to 4000
users having accounts on this cyrus system.  If I
grep "Delivered" in the maillog by the minute I can
see how fast the messages are stored.

e.g.:
# grep Delivered /var/log/maillog | grep 'Jan 23 10:37' | wc -l
    696

That is the best.  This peak event pushed the load to 14
for 12 minutes, where it averages 604 messages
delivered to cyrus mailboxes per minute.  Is that
reasonable for  maximum delivery rate?

I've also backed out the change (yesterday) to
/sys/block/sda/queue/nr_requests
I think it was pushing the load higher and there is no advantage
in my hardware (SAS with Perc 5/i Raid 5 over 4 disk)
to run with a low value for nr_requests.
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