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

[David Mosberger <davidm@napali.hpl.hp.com>]

>>>>> 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.

	--david

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