Date: Mon, 11 Oct 2004 11:56:23 -0400 From: Paul Mather <paul@gromit.dlib.vt.edu> To: freebsd-current@freebsd.org Cc: Chris Elsworth <chris@shagged.org> Subject: Re: RAID1 with gmirror Message-ID: <1097510181.99562.18.camel@zappa.Chelsea-Ct.Org> In-Reply-To: <20041011151506.747E516A4CF@hub.freebsd.org> References: <20041011151506.747E516A4CF@hub.freebsd.org>
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On Mon, 11 Oct 2004 14:26:06 +0100, Chris Elsworth <chris@shagged.org> wrote: > So, I'm left quite unsure whether the warnings are harmless or not. > Pawel, can we just use existing labels on disks and apply a gmirror > over it, or should we be re-labelling inside the mirror device? I believe it is safer to re-bsdlabel the mirror device rather than use an existing disklabel. Remember, the mirror device uses one sector at the end of each provider to store its metadata. So, if you use the existing provider's disklabel, you will at the very least get complaints concerning the label about the "c" partition extending past the end of the device (because the "c" partition will be one sector too long now). Also, if you are unlucky, the mirror metadata might overwrite (and render inaccessible) a sector's worth of actual filesystem data in the last sector from the original provider when you create the mirror. That could cause problems. Labelling the mirror device ensures that filesystem data is not on any inaccessible sectors (assuming you don't deliberately create an invalid label on the new mirror device:). FWIW, I outline in a posting to freebsd-geom the steps I took to do a fresh install of FreeBSD 5.3-BETA to create an root-on-gmirror setup (http://lists.freebsd.org/pipermail/freebsd-geom/2004-September/000307.html). A similar technique could be used to gmirror an existing setup. Cheers, Paul. -- e-mail: paul@gromit.dlib.vt.edu "Without music to decorate it, time is just a bunch of boring production deadlines or dates by which bills must be paid." --- Frank Vincent Zappa
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