Re: Is Read speed faster when 1 disk is failed on raid5 ?

["Yiqiang Ding" <yqding@rasilient.com>]

Hi Jakob,

I don't follow your guesses. Why do you think it may be related to chunk
size? Anyway, I'm using 32K.

yq
----- Original Message -----
From: "Jakob Oestergaard" <jakob@unthought.net>
To: "Yiqiang Ding" <yqding@rasilient.com>
Cc: <raid@ddx.a2000.nu>; <linux-raid@vger.kernel.org>
Sent: Monday, October 28, 2002 1:02 PM
Subject: Re: Is Read speed faster when 1 disk is failed on raid5 ?


> On Mon, Oct 28, 2002 at 10:27:46AM -0800, Yiqiang Ding wrote:
> > I had the similar result with IDE drives through hpt374 controller.
Still
> > don't understand why a degraded system has better read performance.
>
> Could you comment on the guesses I made below, relating to the chunk
> size?
>
> > > Other than that... Well, if the parity information is intact, the
disks
> > > would need to skip the parity blocks when the array is read from
> > > sequentially.  With a degraded array, the reads are all contiguous on
> > > the disks - this could be a difference perhaps??
> > >
> > > What chunk size are you using?  And can you try a chunk size that is
an
> > > order of magnitude bigger or smaller?   (might take some time to test
> > > this out).
> > >
> > > For example, if you use a 4k chunksize (I don't think you do, if my
last
> > > guess holds), then try 128k.  If you are using 64k or above (which,
> > > again, if I am guessing correctly, is probably more like what you're
> > > using), then try 4k.
>
> --
> ................................................................
> :   jakob@unthought.net   : And I see the elder races,         :
> :.........................: putrid forms of man                :
> :   Jakob Østergaard      : See him rise and claim the earth,  :
> :        OZ9ABN           : his downfall is at hand.           :
> :.........................:............{Konkhra}...............:
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