Re: [squid-users] I/O tests and squid

On tis, 2007-08-14 at 11:00 +0800, Ming-Ching Tiew wrote:
> I am having a system which handles about 9000 active sessions
> now, and the iostat result is as such :-
>
> avg-cpu: %user %nice %system %iowait %steal %idle
> 0.92 0.00 1.09 6.16 0.00 91.83
>
> Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn
> sda 67.86 393.10 1233.41 27988252 87818678
> sdb 48.64 152.93 999.94 10888386 71195106
>
> As shown above everything the system is hardly stress in terms of
> CPU. Everything is blocking at I/O - which I am not sure if it is
> disk IO or network IO.

It's not much blocking on disk I/O either, only 6.16%. 91.83% of the
time your server is doing absolutely nothing.

> And it seems the io wait figures is building
> up. I am worried that it will continue to build up and causing bottle
> necking.

There is a significant increase in disk I/O transactions when the cache
has been filled and Squid starts to recycle space. Then it levels out
and stays relative to the amount of cachable traffic you have.

If you use the -x option to iostat then the report is extended by a
number of interesting details. The first one to look at is the %util of
your drive.

iostat -x -i 5

Regards
Henrik