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Date:      Mon, 21 Sep 1998 12:40:25 +0930
From:      Greg Lehey <grog@lemis.com>
To:        Rolandas Miseikis <rol@init.lt>, questions@FreeBSD.ORG
Subject:   Re: ccd mirroring
Message-ID:  <19980921124025.G8807@freebie.lemis.com>
In-Reply-To: <008001bde177$87082e20$1501a8c0@rolandas.init.lt>; from Rolandas Miseikis on Wed, Sep 16, 1998 at 03:40:08PM %2B0200
References:  <008001bde177$87082e20$1501a8c0@rolandas.init.lt>

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On Wednesday, 16 September 1998 at 15:40:08 +0200, Rolandas Miseikis wrote:
> I'm a bit confused about setting ccd interleave factor.
> Could someone explain it in detail or give some pointers?

The idea of interleaving is to even out the load on the drives.  On
the other hand, it also has the potential to increase the overall I/O
load.  In my work (with vinum, see below) I've found that 256 kB is
about right.  I presented a paper on Vinum at the AUUG conference in
Sydney last week, and a guy from Veritas was there.  We discussed this
point, and he seemed to think that 64 kB was a large enough stripe
size, but he works primarily with System V, which may make smaller
transfers.

> And what interleave should I use with CCDF_MIRROR?

256 kB.

Of course, you probably want to use Vinum, which will be in
3.0-RELEASE (next month) and which offers much more flexibility and
(hopefully) fewer chances to shoot yourself in the foot.  Check out
http://www.lemis.com/vinum.html.

Greg
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