From owner-freebsd-doc@FreeBSD.ORG Thu Nov 13 01:04:58 2008 Return-Path: Delivered-To: freebsd-doc@FreeBSD.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id AF400106567F; Thu, 13 Nov 2008 01:04:58 +0000 (UTC) (envelope-from trhodes@FreeBSD.org) Received: from pittgoth.com (pittgoth.com [205.134.163.206]) by mx1.freebsd.org (Postfix) with ESMTP id 800138FC17; Thu, 13 Nov 2008 01:04:57 +0000 (UTC) (envelope-from trhodes@FreeBSD.org) Received: from localhost.fbsdsecure.org (net-ix.gw.ai.net [205.134.160.6]) (authenticated bits=0) by pittgoth.com (8.14.2/8.14.2) with ESMTP id mAD14umj082348 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NOT); Wed, 12 Nov 2008 20:04:57 -0500 (EST) (envelope-from trhodes@FreeBSD.org) Date: Wed, 12 Nov 2008 20:04:54 -0500 From: Tom Rhodes To: "Bob Johnson" Message-Id: <20081112200454.3ddb9b89.trhodes@FreeBSD.org> In-Reply-To: <54db43990811120654l213596f1j844c3f185c3eb577@mail.gmail.com> References: <200811120800.mAC80Cm2038380@freefall.freebsd.org> <54db43990811120654l213596f1j844c3f185c3eb577@mail.gmail.com> X-Mailer: Sylpheed version 1.0.6 (GTK+ 1.2.10; i386-portbld-freebsd8.0) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: trhodes@FreeBSD.org, freebsd-doc@FreeBSD.org Subject: Re: docs/128804: Gmirror handbook instructions convert boot-drive to gmirror, truncating last sector X-BeenThere: freebsd-doc@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Documentation project List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 13 Nov 2008 01:04:58 -0000 On Wed, 12 Nov 2008 09:54:49 -0500 "Bob Johnson" 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 wrote: > > The following reply was made to PR docs/128804; it has been noted by GNATS. > > > > From: Tom Rhodes > > To: Winder > > 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 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