From owner-freebsd-questions@FreeBSD.ORG Tue Oct 13 13:04:47 2009 Return-Path: Delivered-To: freebsd-questions@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id DE9871065692 for ; Tue, 13 Oct 2009 13:04:47 +0000 (UTC) (envelope-from kraduk@googlemail.com) Received: from gv-out-0910.google.com (gv-out-0910.google.com [216.239.58.189]) by mx1.freebsd.org (Postfix) with ESMTP id 69B268FC08 for ; Tue, 13 Oct 2009 13:04:47 +0000 (UTC) Received: by gv-out-0910.google.com with SMTP id n29so2978gve.39 for ; Tue, 13 Oct 2009 06:04:46 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=googlemail.com; s=gamma; h=domainkey-signature:mime-version:received:in-reply-to:references :date:message-id:subject:from:to:cc:content-type; bh=Zhx3Mkjggmx7GZD2EgtbZRqd2u996iAi9RWswyrGU6o=; b=ZbZn2FS/Tpw/4aO7qd3Sap0AmXPJV3YrQF7GD2b1upU9LhUelnlgh4vsVUPcQnN9Q0 PXZI3ZwzOgesB6ILuIfAizmk49zSd3HNArLdanro7Tgor5+X2chXQa+RvmY23CHXDzgu 2sI3N5qBv9wDOnJBDzl5UcIs8n+6iAKTH1F0w= DomainKey-Signature: a=rsa-sha1; c=nofws; d=googlemail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type; b=bFynur4oj3x09SZABw/IzSgAqkVwe+jezv/XNnDOcP1jwx949t9O1DJMJGccoTcwjk 52T/WsWJHtcHNd1nyXfAzg1KPPT8TGjbdzc4Np5ccEEagzqlu8pkPPlH3pVm0IZK6350 vOQ1uELjO3ZgVzZ7IjFVP3XmOG/8ao1siDwx4= MIME-Version: 1.0 Received: by 10.239.139.221 with SMTP id u29mr495898hbu.35.1255439085624; Tue, 13 Oct 2009 06:04:45 -0700 (PDT) In-Reply-To: <59889.1255436565@thrush.ravenbrook.com> References: <59889.1255436565@thrush.ravenbrook.com> Date: Tue, 13 Oct 2009 14:04:45 +0100 Message-ID: From: krad To: Nick Barnes Content-Type: text/plain; charset=ISO-8859-1 X-Content-Filtered-By: Mailman/MimeDel 2.1.5 Cc: freebsd-questions@freebsd.org, Ravenbrook SysAdmins Subject: Re: how does gmirror start up? X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 13 Oct 2009 13:04:47 -0000 2009/10/13 Nick Barnes > I am running a 6.3 system and have had various problems with disk > reliability on a key filesystem, probably down to SCSI hardware or > drivers. I'm intending to replace that SCSI disk with a pair of SATA > disks ad6/7, using gmirror as gm0 (while keeping ad4 as our boot > disk). I have set up the mirror and right now I'm part-way through > using rsync to transfer the data. But I have a question concerning > the underlying operation of GEOM, which is troubling me. I have read > the various man pages and handbook pages relating to GEOM and gmirror, > but they don't seem to answer this. > > When I reboot the system, gmirror comes up (because of the line in > /boot/loader.conf) and gm0 appears, backed by ad6/7. Where is this > configuration information stored? That is, how does the system know > to make gm0, with ad6/7 as the backing store. > > I would expect there to be a file somewhere in /etc with this config > information, but I don't see it in the documentation. From reading > gmirror(8), I understand that there is a label sector at the ends of > ad6 and ad7, identifying them as parts of gm0. But that config > information is back-to-front: at boot time the system knows from > /etc/fstab that it needs gm0; how does it find the underlying disks? > > Does the system search the ends of all physically-attached disks, > looking for GEOM labels, and automatically make any corresponding GEOM > devices? Surely not (that would mean, for instance, that if I took > one of these disks out of this machine and put it into another FreeBSD > system then that machine would automatically set up gm0 with this > disk). > > Possibly I'm just being dense. Can someone enlighten me? > > Nick Barnes > Ravenbrook Limited > _______________________________________________ > freebsd-questions@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-questions > To unsubscribe, send any mail to " > freebsd-questions-unsubscribe@freebsd.org" > you are right there is a label at the end of the disk, and if you put the drives in another machine with another gmirror enabled box it would see the mirror. If you stack geom classes then the label it stored at the end of the container as if it were a disk. eg if you used gjournal on top of gmirror. Its a very common practise for hardware controllers as well. The dell perc controllers definitely have this labelling as you can import foreign configs into the cards nvram from disk