From owner-freebsd-geom@FreeBSD.ORG Sat Sep 17 22:04:16 2005 Return-Path: X-Original-To: freebsd-geom@freebsd.org Delivered-To: freebsd-geom@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id CF92316A41F for ; Sat, 17 Sep 2005 22:04:15 +0000 (GMT) (envelope-from djh@nebcorp.com) Received: from ratchet.nebcorp.com (ratchet.nebcorp.com [205.217.153.72]) by mx1.FreeBSD.org (Postfix) with ESMTP id 9D50143D45 for ; Sat, 17 Sep 2005 22:04:15 +0000 (GMT) (envelope-from djh@nebcorp.com) Received: by ratchet.nebcorp.com (Postfix, from userid 1014) id 4B801D9823; Sat, 17 Sep 2005 15:04:15 -0700 (PDT) Date: Sat, 17 Sep 2005 15:04:15 -0700 From: Danny Howard To: Victor Sudakov Message-ID: <20050917220415.GA73188@ratchet.nebcorp.com> References: <20050916073012.GA31056@admin.sibptus.tomsk.ru> <20050916225527.GT11689@ratchet.nebcorp.com> <20050917041700.GA46650@admin.sibptus.tomsk.ru> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20050917041700.GA46650@admin.sibptus.tomsk.ru> User-Agent: Mutt/1.4.2.1i X-Loop: djhoward@uiuc.edu Cc: freebsd-geom@freebsd.org Subject: Re: Create a mirror on disk with valid data X-BeenThere: freebsd-geom@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: GEOM-specific discussions and implementations List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 17 Sep 2005 22:04:16 -0000 On Sat, Sep 17, 2005 at 11:17:00AM +0700, Victor Sudakov wrote: > Danny Howard wrote: > > > > I have only ever mirrored disks with data on them. Its a question of > > bootstrap - does the mirror comes first or does the data you are going > > to mirror come first? > > Suppose the disk has valuable data in the last sector and you are > going to create a mirror from this disk. What is going to happen when > the last sector is overwritten with the mirror metadata? Your data will > be lost, right? Suppose you need to access the last sector, access > will be denied, right? >From what I have read, the gmirror stuff uses a sector of the disk that isn't used at the end, and if you format a disk in such a way that that free sector is unavailable, you can not set up a gmirror. If you find a scenario in which setting up a gmirror destroys data on a disk, then please use send-pr to file a bug, so that that issue can be fixed. But, if your question is "does gmirror do evil things to existing data" then I'll answer that I and others have gmirrored quite a few disks with existing data and I'm not aware that anybody has been bitten by your hypothesis. Thanks, -danny -- http://dannyman.toldme.com/