High IO Wait - PowerEdge 2650 - Perc 3/Di

Tillotson, Jeff Jeff.Tillotson at KnowledgeStorm.com
Wed Jan 24 13:00:17 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 2.8.1.6098.
>> 
>> 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!
>

Swap usage is low.  In fact, certain instances of this test have no swap
being used.  I have also tried the test with all swap disabled.  Results
are always the same.  

I have also tried re-nicing several process but the results are always
the same.  

Thanks for you response,
Jeff
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