Re: [Gelato-technical] Serious performance degradation on a RAID

[Andreas Hirstius <Andreas.Hirstius@cern.ch>]

David Mosberger wrote:

>>>>>>On Tue, 05 Apr 2005 20:11:51 +0200, Andreas Hirstius <Andreas.Hirstius@cern.ch> said:
>>>>>>            
>>>>>>
>
>  Andreas> Hi, We have a rx4640 with 3x 3Ware 9500 SATA controllers
>  Andreas> and 24x WD740GD HDD in a software RAID0 configuration
>  Andreas> (using md).  With kernel 2.6.11 the read performance on the
>  Andreas> md is reduced by a factor of 20 (!!)  compared to previous
>  Andreas> kernels.  The write rate to the md doesn't change!! (it
>  Andreas> actually improves a bit).
>
>Is there any reason to believe this change in behavior is
>ia64-specific?  I doubt it.  The q-syscollect profiles on your
>web-site shows that the CPU is basically completely idle.  You may
>want to try 2.6.10 to see whether the bad behavior was introduced
>before or after that.  Unfortunately, 2.6 is developing very rapidly
>so you may have to do more binary searching between 2.6.9 and 2.6.10
>or 2.6.10 and 2.6.11 to pin the problem down to a useful granularity.
>You may also want to look at the bitkeeper changelogs to see if you
>can find anything suspicious (you can do that easily via the web by
>browsing the source code [1]).  Lastly, you may want to ask on
>linux-kernel whether anybody can think of a change that could have
>this effect.
>
>  
>
The problems started with 2.6.10-bk7...
(and I've tested 2.6.9, 2.6.10, 2.6.10-bk5 - -bk14,  2.6.11-rc[1-5], 
2.6.11, 2.6.11-mm[12], 2.6.12-rc[12])

The only other platform I have is a dual-xeon and I don't see the 
problem there (same controllers/disks)...

Because of this strange correlation between block size and page size and 
the fact, that I don't see a problem on x86 I suspected an ia64-specific 
problem. My "favourite" candidate is the conversion to 4 level 
pagetables between 2.6.10-bk6 and 2.6.10-bk7.


Andreas


>	--david
>
>[1] http://linux.bkbits.net:8080/linux-2.5/src?nav=index.html
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