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Re: poor io performance with xfs+raid5

To: Justin Coffey <justin@xxxxxxxxx>
Subject: Re: poor io performance with xfs+raid5
From: Seth Mos <knuffie@xxxxxxxxx>
Date: Fri, 26 Apr 2002 07:28:03 +0200 (CEST)
Cc: Steve Lord <lord@xxxxxxx>, Mike Eldridge <diz@xxxxxxxxx>, <linux-xfs@xxxxxxxxxxx>
In-reply-to: <Pine.BSO.4.44.0204251220310.25324-100000@xxxxxxxxxxxxxxxxxxxxxxxxxx>
Sender: owner-linux-xfs@xxxxxxxxxxx
On Thu, 25 Apr 2002, Justin Coffey wrote:

>
> > The alignment issue is mostly software raid5 specific. The ability to
> > better align the writes will help on other configs to a lesser extent.
>
> Thanks.  We're in the design phase of a new product and it's likely to use
> some sort of largish NAS box.  Most likely raid 5'ed.  Initially (due to
> cost) we'll probably do software raid but we'll want to move to hardware
> level at some point.  I guess that means ReiserFS for us for now?

Only software raid is affected by the unaligned access. If you use
hardware raid like the escalade has there shouldn't be a problem.

I have a 3disk software raid5 volume which performs reasonable even with
thye current code base.

Can you give some number about the disk performance?

If you really need fast IO you should look into raid 1 or 10. These have a
lot lower overhead then raid5. The card may be the limiting factor.

Cheers
Seth


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