From owner-freebsd-geom@FreeBSD.ORG Mon Sep 19 08:56:33 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 977F816A41F for ; Mon, 19 Sep 2005 08:56:33 +0000 (GMT) (envelope-from sudakov@sibptus.tomsk.ru) Received: from relay2.tomsk.ru (relay2.tomsk.ru [212.73.124.8]) by mx1.FreeBSD.org (Postfix) with ESMTP id C560043D46 for ; Mon, 19 Sep 2005 08:56:32 +0000 (GMT) (envelope-from sudakov@sibptus.tomsk.ru) X-Virus-Scanned: by Dr.Web (R) daemon for FreeBSD, version 4.32.1 (2004-08-30) at relay2.tomsk.ru Received: from [172.16.138.125] (account sudakovva@sibptus.tomsk.ru HELO admin.sibptus.tomsk.ru) by relay2.tomsk.ru (CommuniGate Pro SMTP 4.3.2) with ESMTPSA id 1214920; Mon, 19 Sep 2005 15:56:25 +0700 Received: (from sudakov@localhost) by admin.sibptus.tomsk.ru (8.12.9p2/8.12.9/Submit) id j8J8uP4k074159; Mon, 19 Sep 2005 15:56:25 +0700 (OMSST) (envelope-from sudakov) Date: Mon, 19 Sep 2005 15:56:25 +0700 From: Victor Sudakov To: Danny Howard Message-ID: <20050919085625.GF73933@admin.sibptus.tomsk.ru> 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 Organization: AO "Svyaztransneft", SibPTUS X-PGP-Key: http://vas.tomsk.ru/vas.asc 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: Mon, 19 Sep 2005 08:56:33 -0000 Victor Sudakov 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? I have done some experimenting and found out the following. If you plan to put data onto a disk first, and convert the disk into a mirror later, the disk should be from the very beginning labelled so that the area for data is one sector smaller than disklabel suggests. If this condition is met, I believe converting a disk with data into a mirror is safe. -- Victor Sudakov, VAS4-RIPE, VAS47-RIPN