Date: Wed, 12 Nov 2008 20:04:54 -0500 From: Tom Rhodes <trhodes@FreeBSD.org> To: "Bob Johnson" <fbsdlists@gmail.com> Cc: trhodes@FreeBSD.org, freebsd-doc@FreeBSD.org Subject: Re: docs/128804: Gmirror handbook instructions convert boot-drive to gmirror, truncating last sector Message-ID: <20081112200454.3ddb9b89.trhodes@FreeBSD.org> In-Reply-To: <54db43990811120654l213596f1j844c3f185c3eb577@mail.gmail.com> References: <200811120800.mAC80Cm2038380@freefall.freebsd.org> <54db43990811120654l213596f1j844c3f185c3eb577@mail.gmail.com>
next in thread | previous in thread | raw e-mail | index | archive | help
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? > > > 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
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20081112200454.3ddb9b89.trhodes>