Subject: Re: Low AAC performance but only when tested through the file system
To: Olaf Seibert <>
From: Bill Studenmund <>
List: current-users
Date: 12/01/2003 17:57:30
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On Mon, Dec 01, 2003 at 02:50:52AM +0100, Olaf Seibert wrote:
> On Sun 30 Nov 2003 at 15:07:33 -0800, Bill Studenmund wrote:
> > What's your stripe depth? For optimal performance, you want it to be 16=
k. =20
> > The file system will do 64k i/o's. With 4 data drives & a 16k stripe
> > depth, a 64k i/o (on a 64k boundary) will hit all 4 drives at once.
> It's the default 64k. In the previous hardware I tried 16k also but it
> made no difference, so I never tried it on this one.

With a stripe depth of 64k (stripe width of 256k) and 64k i/os you will  =
get poor performance. If you are performing random i/o, each of those 64k=
writes means READING 3 * 64k =3D 192k then writing 128k.

Assuming the stripe depth really is 64k, each write by the OS will turn=20
into a read/modify/write operation in the RAID card. You'll be getting=20
worse performance than if you just used one drive.

I think you want to try playing with RAID tuning.

Take care,


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