Re: iostat with raid device...

[NeilBrown <neilb@suse.de>]

On Wed, 13 Apr 2011 11:21:52 -0700 Linux Raid Study
<linuxraid.study@gmail.com> wrote:

> Let me reword previous email...
> 
> I tried to change stripe_cache_size as following and tried values
> between 16 to 4096
> echo 512 > /sys/block/md0/md/stripe_cache_size
> 
> But, I'm not seeing too much difference in performance. I'm running on
> 2.6.27sh kernel.

I wouldn't expect much difference.

> 
> Any ideas...

On what exactly?
What exactly are you doing, what exactly are the results?  What exactly don't
you understand?

Detail help.

NeilBrown



> 
> Thanks for your help...
> 
> On Tue, Apr 12, 2011 at 12:36 PM, Linux Raid Study
> <linuxraid.study@gmail.com> wrote:
> > Hello Neil,
> >
> > For the benchmarking purpose, I've configured array of ~30GB.
> > stripe_cache_size is 1024 (so 1M).
> >
> > BTW, I'm using Windows copy (robocopy) utility to test perf and I
> > believe block size it uses is 32kB. But since everything gets written
> > thru VFS, I'm not sure how to change stripe_cache_size to get optimal
> > performance with this setup...
> >
> > Thanks.
> >
> > On Mon, Apr 11, 2011 at 7:51 PM, NeilBrown <neilb@suse.de> wrote:
> >> On Mon, 11 Apr 2011 18:57:34 -0700 Linux Raid Study
> >> <linuxraid.study@gmail.com> wrote:
> >>
> >>> If I use --assume-clean in mdadm, I see performance is 10-15% lower as
> >>> compared to the case wherein this option is not specified. When I run
> >>> without --assume_clean, I wait until mdadm prints "recovery_done" and
> >>> then run IO benchmarks...
> >>>
> >>> Is perf drop expected?
> >>
> >> No.  And I cannot explain it.... unless the array is so tiny that it all fits
> >> in the stripe cache (typically about 1Meg).
> >>
> >> There really should be no difference.
> >>
> >> NeilBrown
> >>
> >

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