High IO Wait - PowerEdge 2650 - Perc 3/Di

Stephen Carville stephen at totalflood.com
Fri Jan 19 09:08:03 CST 2007

Tillotson, Jeff wrote:
> Hello all,
> I have a Dell 2650 with a RAID1 drive connected to a Dell PowerEdge
> Expandable RAID controller 3/Di on a SuSE Enterprise Linux 9.3 server
> running 2.6.5-7.283-bigsmp #1 SMP Wed Nov 29 16:55:53 UTC 2006 i686 i686
> i386 GNU/Linux.
> The system is hanging during or after file writes.  If I do something
> like:
> dd if=/dev/zero of=/home/jefft/file1 bs=512 count=864000 the system will
> eventually hang and come back.  Using sar, iostat, top, I can watch
> iowait
> percentage climb and climb until it hangs.  Then, when I can gain access
> again, it drops slowly.  The iowait percentage goes up even after the dd
> has completed.
> I have updated the PERC's firmware to
> There is no error messages in dmesg, log messages or anyplace else.  Is
> there
> some mechanism for tuning this?  Any help would be greatly appreciated.

Is swap usage low?  Do kscand and kswapd consistently show high in the 
list on top when sorted by CPU usage?

Try re-nicing kscand to 19 and observe the effect.  If that doesn't 
cause any problems, then re-nice kswapd to 19.

The above can be dangerous to do if swap usage is high so be careful!

Stephen Carville <stephen at totalflood.com>
Unix and Network Admin
Nationwide Totalflood
6033 W. Century Blvd
Los Angeles, CA 90045

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