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Date:      Thu, 5 Aug 2004 09:25:22 +0200
From:      Stijn Hoop <stijn@win.tue.nl>
To:        "H. Sandring" <h.sandring@gmx.net>
Cc:        freebsd-questions@freebsd.org
Subject:   Re: RAID 5 stripe size
Message-ID:  <20040805072521.GH43462@pcwin002.win.tue.nl>
In-Reply-To: <003601c47aba$2dd9ca10$0501a8c0@kojo>
References:  <003601c47aba$2dd9ca10$0501a8c0@kojo>

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Hi,

On Thu, Aug 05, 2004 at 03:02:25PM +0800, H. Sandring wrote:
> Is there an intelligent way of choosing the stripe size of a RAID 5
> array?

=46rom man vinum:

"For optimum performance, stripes should be at least 128 kB in size: anythi=
ng
smaller will result in a significant increase in I/O activ- ity due to mapp=
ing
of individual requests over multiple disks.  The performance improvement due
to the increased number of concurrent transfers caused by this mapping will
not make up for the performance drop due to the increase in latency.  A good
guideline for stripe size is between 256 kB and 512 kB.  Avoid powers of 2,
however: they tend to cause all superblocks to be placed on the first subdi=
sk."

I expect this to be true for non-vinum RAID-5 volumes as well.

HTH,

--Stijn

--=20
The most reliable proof that there are extraterrestrial intelligent
lifeforms out there is that nobody actually tries to get in contact
with us.
		-- Dirk Mueller

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