On Fri, Jan 18, 2008 at 11:01:11AM -0800, Martin Knoblauch wrote:
quoted text
>  At least, rc1-rc5 have shown that the CCISS system can do well. Now
> the question is which part of the system does not cope well with the
> larger IO sizes? Is it the CCISS controller, LVM or both. I am open to
> suggestions on how to debug that. 

What is your LVM device configuration?
  E.g. 'dmsetup table' and 'dmsetup info -c' output.
Some configurations lead to large IOs getting split up on the way through
device-mapper.

See if these patches make any difference:
  http://www.kernel.org/pub/linux/kernel/people/agk/patches/2.6/editing/

    dm-md-merge_bvec_fn-with-separate-bdev-and-sector.patch
    dm-introduce-merge_bvec_fn.patch
    dm-linear-add-merge.patch
    dm-table-remove-merge_bvec-sector-restriction.patch
 
Alasdair
-- 
agk@redhat.com
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