Re: Linux filesystem speed comparison

From: Henrik Nordstrom <>
Date: Mon, 11 Apr 2005 12:08:49 +0200 (CEST)

On Mon, 11 Apr 2005, Steven Wilton wrote:

> We are running some large proxies in our Melbourne POP, and we graph the CPU
> counters available in the 2.6 linux kernel to give us an idea of what the
> CPU is doing. We noticed that the CPU was spending large amounts of time
> (around 60%) in an I/O wait state, which is when the CPU is idle, but there
> are pending disk i/o opeartions.

Which as such isn't that harmful to Squid (aufs/diskd) as Squid continues
processing requests while there is pending I/O request. But on the other
hand when the disk %util level approaches 100 you reach the limit of what
the drive can sustain.

The more work Squid is having the less %iowait you should be seeing due to
Squid (and other tasks) making use of that CPU time. For this reason it
is better to measure the disk %util rather than the system %iowait.

In the CPU utilization you should sum %iowait and %idle as idle CPU time.
%user and %sys is interesting.

Note: %util is reported by iostat -x.

Received on Mon Apr 11 2005 - 04:08:52 MDT

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