Date: Wed, 12 Nov 2008 08:00:12 GMT From: Tom Rhodes <trhodes@FreeBSD.org> To: freebsd-doc@FreeBSD.org Subject: Re: docs/128804: Gmirror handbook instructions convert boot-drive to gmirror, truncating last sector Message-ID: <200811120800.mAC80Cm2038380@freefall.freebsd.org>
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The following reply was made to PR docs/128804; it has been noted by GNATS. From: Tom Rhodes <trhodes@FreeBSD.org> To: Winder <freebsdbugs.20.awinder@spamgourmet.com> Cc: freebsd-gnats-submit@FreeBSD.org Subject: Re: docs/128804: Gmirror handbook instructions convert boot-drive to gmirror, truncating last sector Date: Wed, 12 Nov 2008 02:18:59 -0500 On Wed, 12 Nov 2008 01:21:55 GMT Winder <freebsdbugs.20.awinder@spamgourmet.com> wrote: Hi, > > >Number: 128804 > >Category: docs > >Synopsis: Gmirror handbook instructions convert boot-drive to gmirror, truncating last sector > >Confidential: no > >Severity: non-critical > >Priority: medium > >Responsible: freebsd-doc > >State: open > >Quarter: > >Keywords: > >Date-Required: > >Class: doc-bug > >Submitter-Id: current-users > >Arrival-Date: Wed Nov 12 01:30:01 UTC 2008 > >Closed-Date: > >Last-Modified: > >Originator: Winder > >Release: 7.1-PRERELEASE > >Organization: > >Environment: > FreeBSD DEV2 7.1-PRERELEASE FreeBSD 7.1-PRERELEASE #3: Fri Nov 7 19:54:41 MST 2008 windrider@DEV2:/usr/obj/usr/src/sys/packetcheckv1-fileserv amd64 > >Description: > http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/geom-mirror.html > > This geom mirroring documentation shows a way to convert the boot drive into a gmirror raid. This guide misleads in assuming your whole drive has not been used. > > The problem is that gmirror truncates the last sector of the drive for metadata; thus, any data stored in that sector when adding the drive into the RAID is lost. Sysinstall uses the entire drive by default. Following these instructions, then, could cause loss of data or a corrupt partition, as it will reach one sector beyond the end of the geom mirror device. > > mightn't it be better to make an example from a blank disk? I would think that converting the disk device to a software RAID, at least the boot disk, would be the way most people wanted to use it. And in most cases, I think that it's one of the first things done during an installation - though, YMMV. If the last sector is filled with user data - there are larger problems, possibly, than just where GEOM places metadata. If you feel a warning is required here, I'll gladly add one, but it never crossed my mind initially that someone would actually be using the last sector on the drive for data. Thanks, -- Tom Rhodes
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