From owner-freebsd-stable  Wed Sep  5 14:40:58 2001
Delivered-To: freebsd-stable@freebsd.org
Received: from freeway.dcfinc.com (cx74889-a.phnx3.az.home.com [24.1.193.157])
	by hub.freebsd.org (Postfix) with ESMTP
	id B781537B409; Wed,  5 Sep 2001 14:40:55 -0700 (PDT)
Received: (from chad@localhost)
	by freeway.dcfinc.com (8.8.8/8.8.8) id OAA06525;
	Wed, 5 Sep 2001 14:40:34 -0700 (MST)
	(envelope-from chad)
Date: Wed, 5 Sep 2001 14:40:34 -0700
From: "Chad R. Larson" <chad@DCFinc.com>
To: David Gilbert <dgilbert@velocet.ca>
Cc: Doug Hardie <bc979@lafn.org>,
	Lawrence Farr <l.farr@epcdirect.co.uk>,
	"'Greg Lehey'" <grog@FreeBSD.ORG>,
	"'Lawrence Farr'" <lawrence@epcdirect.co.uk>,
	"'Chris BeHanna'" <behanna@zbzoom.net>,
	"'FreeBSD-Stable'" <stable@FreeBSD.ORG>
Subject: Re: [stable] Re: RAID5
Message-ID: <20010905144034.C6345@freeway.dcfinc.com>
References: <002c01c135e4$69c924d0$c80aa8c0@lfarr> <f04330116b7bbe195e610@[10.0.1.100]> <15254.16593.350305.548246@trooper.velocet.net>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
User-Agent: Mutt/1.2.5i
In-Reply-To: <15254.16593.350305.548246@trooper.velocet.net>; from dgilbert@velocet.ca on Wed, Sep 05, 2001 at 11:12:17AM -0400
Sender: owner-freebsd-stable@FreeBSD.ORG
Precedence: bulk
List-ID: <freebsd-stable.FreeBSD.ORG>
List-Archive: <http://docs.freebsd.org/mail/> (Web Archive)
List-Help: <mailto:majordomo@FreeBSD.ORG?subject=help> (List Instructions)
List-Subscribe: <mailto:majordomo@FreeBSD.ORG?subject=subscribe%20freebsd-stable>
List-Unsubscribe: <mailto:majordomo@FreeBSD.ORG?subject=unsubscribe%20freebsd-stable>
X-Loop: FreeBSD.ORG

On Wed, Sep 05, 2001 at 11:12:17AM -0400, David Gilbert wrote:
> Now imagine the softupdates case:  If the RAID-5 information was
> managed by softupdates (or similar system), we could identify multiple 
> updates to blocks in the same RAID group at the filesystem level and
> avoid as many as 6 of the 14 writes.  Moreover, this might actually be 
> managed at the buffer-cache level instead of the current system where
> the blocks are forced out to disk synchronously.

Large commercial disk farms such as the EMC Symetrics or the Sun
A3500 do something like that.  They have ECC memory with it's own
battery back up, and the reads and writes are to that memory.  The
hard drives are basically backing store for the RAM.

	-crl
--
Chad R. Larson (CRL15)   602-953-1392   Brother, can you paradigm?
chad@dcfinc.com         chad@larsons.org          larson1@home.com
DCF, Inc. - 14623 North 49th Place, Scottsdale, Arizona 85254-2207

To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-stable" in the body of the message