Re: unbelievably bad performance: 2.6.27.37 and raid6

[Thomas Fjellstrom <tfjellstrom@shaw.ca>]

On Sun November 1 2009, NeilBrown wrote:
> On Mon, November 2, 2009 6:41 am, Thomas Fjellstrom wrote:
> > On Sun November 1 2009, Andrew Dunn wrote:
> >> Are we to expect some resolution in newer kernels?
> >
> > I assume all of the new per-bdi-writeback work going on in .33+ will
> > have a
> > large impact. At least I'm hoping.
> >
> >> I am going to rebuild my array (backup data and re-create) to modify
> >> the chunk size this week. I hope to get a much higher performance when
> >> increasing from 64k chunk size to 1024k.
> >>
> >> Is there a way to modify chunk size in place or does the array need to
> >> be re-created?
> >
> > This I'm not sure about. I'd like to be able to reshape to a new chunk
> > size
> > for testing.
> 
> Reshaping to a new chunksize is possible with the latest mdadm and
>  kernel, but I would recommend waiting for mdadm-3.1.1 and 2.6.32.
> With the current code, a device failure during reshape followed by an
> unclean shutdown while reshape is happening can lead to unrecoverable
> data loss.  Even a clean shutdown before the shape finishes in that case
> might be a problem.

That's good to know. Though I'm stuck with 2.6.26 till the performance 
regressions in the io and scheduling subsystems are solved.

> NeilBrown
> 
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-- 
Thomas Fjellstrom
tfjellstrom@shaw.ca