From owner-freebsd-stable@FreeBSD.ORG Tue Apr 4 21:51:14 2006 Return-Path: X-Original-To: stable@freebsd.org Delivered-To: freebsd-stable@FreeBSD.ORG Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 5A5CD16A401 for ; Tue, 4 Apr 2006 21:51:14 +0000 (UTC) (envelope-from mikej@rogers.com) Received: from smtp101.rog.mail.re2.yahoo.com (smtp101.rog.mail.re2.yahoo.com [206.190.36.79]) by mx1.FreeBSD.org (Postfix) with SMTP id 7A40943D49 for ; Tue, 4 Apr 2006 21:51:13 +0000 (GMT) (envelope-from mikej@rogers.com) Received: (qmail 93332 invoked from network); 4 Apr 2006 21:51:12 -0000 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=rogers.com; h=Received:Message-ID:Date:From:User-Agent:MIME-Version:To:CC:Subject:References:In-Reply-To:Content-Type:Content-Transfer-Encoding; b=3R/jRljUf7Xd6ff+6yTJEl1W68uvT0Pw5UHBqap19Kj+bO38fRj/PAMFLJECeYb7yyan8BVmmAT+a5zLfHbPXg61icAyejCLXiN/qr9zbvM4cIKgJGVbNAF4fzsctSD9n5iBwDQV1Ll4b4Pa7nU+cw46ZF1oHjNDytYlO8JiiXw= ; Received: from unknown (HELO ?70.31.50.218?) (mikej@rogers.com@70.31.50.218 with plain) by smtp101.rog.mail.re2.yahoo.com with SMTP; 4 Apr 2006 21:51:12 -0000 Message-ID: <4432EA5E.3060003@rogers.com> Date: Tue, 04 Apr 2006 17:51:26 -0400 From: Mike Jakubik User-Agent: Thunderbird 1.5 (Windows/20051201) MIME-Version: 1.0 To: Eric Anderson References: <440D74B3.3030309@vwsoft.com> <200603070939.30032.joao@matik.com.br> <54559.192.168.0.10.1141751042.squirrel@webmail.sd73.bc.ca> <20060316160813.GA15720@nowhere> <442033A2.2030208@rogers.com> <442043D0.6090206@centtech.com> In-Reply-To: <442043D0.6090206@centtech.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: stable@freebsd.org, pjd@freebsd.org, Craig Boston Subject: Re: gmirror on existing filesystem (was Fresh install on gmirror'ed disks?) X-BeenThere: freebsd-stable@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Production branch of FreeBSD source code List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 04 Apr 2006 21:51:14 -0000 Eric Anderson wrote: > Mike Jakubik wrote: >> Craig Boston wrote: >>> On Tue, Mar 07, 2006 at 09:04:02AM -0800, Freddie Cash wrote: >>> >>>> There's no need to copy files around. gmirror handles it all for you >>>> behind the scenes. Just create the gmirror labels using the existing >>>> disks/slices/partitions, then insert the second set of >>>> disks/slices/parittions. gmirror will handle synchonising the data >>>> across the mirror. >>>> >>> >>> AFAIK, gmirror causes whatever provider it's mirroring to "lose" the >>> last block to metadata. I've always avoided mirroring an existing >>> filesystem for fear that shrinking a UFS filesystem's underlying device >>> might cause problems down the road. >>> >>> Can someone with knowledge of the UFS internals please confirm one way >>> or the other if this is dangerous or not? >>> >> >> I'm curious to know this as well, as i have some systems using >> gmirror, that were setup in this fashion. Could someone knowledgeable >> on the matter shed some light? > > > I've gmirrored existing disks/slices before, and it's worked fine. > I'm not 100% certain about all cases, but it's possible that the > filesystem could be right up against the last block of the partition, > and it could get stomped on I suppose. > > I'm not sure what this command tells you for sure, but it dumps the > last block of a slice, or disk, or whatever: > > > dd if=/dev/ad0s3a iseek=`diskinfo ad0s3a | perl -ne '@d = split; print > ($d[2]/$d[1] - 1)'` count=512 | hexdump Could someone provide an authoritative answer to this please? Pawel, it would be nice to see some support for your own code from you. This is a very easy method to create a mirror on an existing system, but if its going to cause problems then its useless (All the more reason for geom enabled installer).