Re: stripe_cache_size and performance

[Raz <raziebe@gmail.com>]

On 6/22/07, Jon Nelson <jnelson-linux-raid@jamponi.net> wrote:
> On Thu, 21 Jun 2007, Raz wrote:
>
> > What is your raid configuration ?
> > Please note that the stripe_cache_size is acting as a bottle neck in some
> > cases.
>
> Well, it's 3x SATA drives in raid5. 320G drives each, and I'm using a
> 314G partition from each disk (the rest of the space is quiescent).
what is the chunk size ?. Please note that a raid performance is dependent
on the access pattern to the disks. What is this raid aimed to do ?
more reads ? more writes ? If you can control the access pattern ,
you might be able to increase performance.
> > On 6/21/07, Jon Nelson <jnelson-linux-raid@jamponi.net> wrote:
> > >
> > > I've been futzing with stripe_cache_size on a 3x component raid5,
> > > using 2.6.18.8-0.3-default on x86_64 (openSUSE 10.2).
> > >
> > > With the value set at 4096 I get pretty great write numbers.
> > > 2048 and on down the write numbers slowly drop.
> > >
> > > However, at values above 512 the 'check' performance is terrible. By
> > > 'check' performance I mean the value displayed by /proc/mdstat after
> > > I issue:
> > >
> > > echo check > /sys/block/md0/md/sync_action
> > >
> > > When I say "terrible" I mean < 3MB/s.
> > > When I use 384, the performance goes to ~70MB/s
> > > 512.. 72-73MB/s
> > > 640.. 73-74MB/s
> > >
> > > 768.. 3300 K/s. Wow!
> > >
> > > Can somebody 'splain to me what is going on?
> > >
> > > --
> > > Jon Nelson <jnelson-linux-raid@jamponi.net>
> > > -
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> > >
> >
> >
> > --
> > Raz
> >
> >
> >
>
> --
> Jon Nelson <jnelson-linux-raid@jamponi.net>
> -
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>


-- 
Raz