From: Damir Delija (damir.delija@PBZ.HR)
Date: Fri Apr 09 2004 - 03:10:09 EDT
> -----Original Message-----
> From: Jason delaFuente [ mailto:jason.delafuente@GBE.COM]
> Sent: Thursday, April 08, 2004 4:52 PM
> To: aix-l@Princeton.EDU
> Subject: IO WAIT Information From IBM
[snip]
>
>
> Conclusion:
>
> The iowait statistic may or may not be a useful indicator of
> I/O performance - but it does tell us that the system can
> handle more computational work. Just because a CPU is in
> iowait state does not mean that it can't run other threads
> on that CPU; that is, iowait is simply a form of idle time.
>
>
> Jason de la Fuente
>
In fact huge iowait is sign of the serious trouble - it means that system is
waiting for io to finish so there is probalby user response time impact.
Here is one daily graph (I hope it wil pass trough)
where iow is about 50% during work hours, almost sum of usr and sys. It is 14 CPU 14GB LPAR on P690 with SAN disks
This is oracle database server and apllication users get serious slow downs during day. So despite machine is actually 50% free
there is a problem. In this special case problem is caused by disk layout (whole oracle instnce cca 300GB is on one disk and one filesystem)
and application code wcich generates hot spots in the tables.
Damir
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