Date: Wed, 12 Nov 2008 22:04:31 -0500 From: Tom Rhodes <trhodes@FreeBSD.org> To: Tom Rhodes <trhodes@FreeBSD.org> Cc: freebsd-doc@FreeBSD.org Subject: Re: docs/128804: Gmirror handbook instructions convert boot-drive to gmirror, truncating last sector Message-ID: <20081112220431.3e451c3e.trhodes@FreeBSD.org> In-Reply-To: <20081112200454.3ddb9b89.trhodes@FreeBSD.org> References: <200811120800.mAC80Cm2038380@freefall.freebsd.org> <54db43990811120654l213596f1j844c3f185c3eb577@mail.gmail.com> <20081112200454.3ddb9b89.trhodes@FreeBSD.org>
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On Wed, 12 Nov 2008 20:04:54 -0500 Tom Rhodes <trhodes@FreeBSD.org> wrote: > On Wed, 12 Nov 2008 09:54:49 -0500 > "Bob Johnson" <fbsdlists@gmail.com> wrote: > > > The user has no control over whether the last sector of the drive is > > used for data. Data is scattered all over the drive, in something that > > resembles a random fashion, and I know of no reason the last sector is > > not just as likely to have data stored to it as any other sector on > > the drive (but I am certainly not an authority on the filesystem > > algorithms). > > > > I think a warning is very much in order (that there is a small chance > > that data will be lost by this procedure). > > > > - Bob > > > Don't Unix file systems attempt to lump data closer together > in order to reduce this fragmentation which scatters data > across the entire drive, making it unlikely to have data in > that last sector unless one went beyond the 8% boundry? Sorry, I really hope this didn't come off as rude. While I know the user has no control over where data is stored on the hard disk, I would also assume a warning about this to be in the manual page as well. It's very possible that the metadata is stored in a location not touchable by a filesystem. Thus, I have sent an email to Pawel for further examination. Thanks, > > > > > > > > On 11/12/08, Tom Rhodes <trhodes@freebsd.org> wrote: > > > 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 > > > _______________________________________________ > > > freebsd-doc@freebsd.org mailing list > > > http://lists.freebsd.org/mailman/listinfo/freebsd-doc > > > To unsubscribe, send any mail to "freebsd-doc-unsubscribe@freebsd.org" > > > > > > > > > -- > > -- Bob Johnson > > fbsdlists@gmail.com > > _______________________________________________ > > freebsd-doc@freebsd.org mailing list > > http://lists.freebsd.org/mailman/listinfo/freebsd-doc > > To unsubscribe, send any mail to "freebsd-doc-unsubscribe@freebsd.org" > > > > > -- > Tom Rhodes > -- Tom Rhodes
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