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:
- 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.