From owner-freebsd-hackers@FreeBSD.ORG  Sun Nov  9 13:36:22 2003
Return-Path: <owner-freebsd-hackers@FreeBSD.ORG>
Delivered-To: freebsd-hackers@freebsd.org
Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125])
	by hub.freebsd.org (Postfix) with ESMTP
	id 70F7716A4CE; Sun,  9 Nov 2003 13:36:22 -0800 (PST)
Received: from VARK.homeunix.com (adsl-68-123-40-77.dsl.pltn13.pacbell.net
	[68.123.40.77])	by mx1.FreeBSD.org (Postfix) with ESMTP
	id 942B943F75; Sun,  9 Nov 2003 13:36:21 -0800 (PST)
	(envelope-from das@FreeBSD.ORG)
Received: from VARK.homeunix.com (localhost [127.0.0.1])
	by VARK.homeunix.com (8.12.9/8.12.9) with ESMTP id hA9LYpen014114;
	Sun, 9 Nov 2003 13:34:51 -0800 (PST)
	(envelope-from das@FreeBSD.ORG)
Received: (from das@localhost)
	by VARK.homeunix.com (8.12.9/8.12.9/Submit) id hA9LYo39014113;
	Sun, 9 Nov 2003 13:34:50 -0800 (PST)
	(envelope-from das@FreeBSD.ORG)
Date: Sun, 9 Nov 2003 13:34:50 -0800
From: David Schultz <das@FreeBSD.ORG>
To: Christian Laursen <xi@borderworlds.dk>
Message-ID: <20031109213450.GB13982@VARK.homeunix.com>
Mail-Followup-To: Christian Laursen <xi@borderworlds.dk>,
	Lukas Ertl <l.ertl@univie.ac.at>, hackers@FreeBSD.ORG,
	phk@FreeBSD.ORG
References: <20031109003617.K626@korben.in.tern>
	<20031109023041.GA9171@VARK.homeunix.com>
	<868ympydcx.fsf@borg.borderworlds.dk>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <868ympydcx.fsf@borg.borderworlds.dk>
cc: hackers@FreeBSD.ORG
cc: phk@FreeBSD.ORG
cc: Lukas Ertl <l.ertl@univie.ac.at>
Subject: Re: geom_mirror implementation
X-BeenThere: freebsd-hackers@freebsd.org
X-Mailman-Version: 2.1.1
Precedence: list
List-Id: Technical Discussions relating to FreeBSD
	<freebsd-hackers.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-hackers>,
	<mailto:freebsd-hackers-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-hackers>
List-Post: <mailto:freebsd-hackers@freebsd.org>
List-Help: <mailto:freebsd-hackers-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-hackers>,
	<mailto:freebsd-hackers-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Sun, 09 Nov 2003 21:36:22 -0000

On Sun, Nov 09, 2003, Christian Laursen wrote:
> David Schultz <das@FreeBSD.ORG> writes:
> 
> > On Sun, Nov 09, 2003, Lukas Ertl wrote:
> > > Hi hackers@,
> > > 
> > > I've played around with GEOM a bit and beefed up geom_mirror, which is
> > > already in the tree but not built yet.
> > > 
> > > You can find the patch at <http://mailbox.univie.ac.at/~le/geom.diff>.
> > 
> > Hmm...I believe geom_mirror is supposed to be an example, and
> > geom_ccd is supposed to be the production mirroring implementation.  
> > ccd does have its quirks, though...
> 
> Last time I checked ccd needed to be manually reconfigured to run in
> degraded mode and sync is not possible. In my book that's not good
> enough for production.
> 
> Furthermore it would be nice with a mirror implementation that
> automatically syncs the mirror after an unclean shutdown.

Yeah, RAID support in FreeBSD is in a rather sorry state right
now.  ccd(4) doesn't work with ATAng on my machine without causing
panics and data corruption, raidframe is broken in -CURRENT, and
vinum tends to lag behind changes and break.  But that doesn't
mean that the right solution is to add a *fourth* incompatible
RAID implementation.  If there's a good reason ccd(4) is harder to
fix than geom_mirror, then you might want to talk to phk about
rewriting geom_ccd based on geom_mirror.  I believe scottl and phk
have plans to fix raidframe, though, which would address a lot of
the present limitations.