On 11-07-11 5:03 PM, Stan Hoeppner wrote:
Given that you're running Dovecot 1.0.15 I'm guessing you're using
CentOS or RHEL 5.x and thus have kernel 2.6.18-xxx. 2.6.18 is 5 years
old now and not inappropriate for a modern 2 socket, 6 core
HyperThreading box. You need a much newer kernel, preferably in the
2.6.3x series. 2.6.18 could be reporting incorrect load numbers on
these machines.
RHEL kernel version numbers do not say much. The redhat 2.6.18 is 2.6.18
+ a boatload of "enterprise load" patches and backports from 2.6.2x.
OTOH, dovecot 1.0.15 is ancient indeed :)
The discrepancies lie in two areas:
1) Load Average
On Linux, load average strictly shows total system CPU usage in
intervals, nothing else.
That would be FreeBSD, AFAIK. On linux, I/O does add to the load
average. A process in state 'D' (Disk wait, could be NFS wait too btw)
adds '1' to the load. If you have a broken NFS server and 2000 processes
waiting on I/O, the reported load will go over 2000.
You get a better impression of system load by running 'top' and paying
attention to the number on the 'cpu' line: us == time spent in user
process, sy = kernel, id = idle, wa = I/O wait, si = interrupts
Press '1' while in top to expand the view to all CPUs seperately. Quite
enlightening.
Given that all mail apps are 100% IO bound, never CPU or memory bound,
I'd guess you'll never see a load average over 4.00 on any of these
machines with less than 1000 concurrent connections.
Well, see above. Also, if you have SSL enabled, the crypto will actually
eat quite a bit of CPU if you have a lot of network traffic.
Mike.
