From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx1.redhat.com (ext-mx13.extmail.prod.ext.phx2.redhat.com [10.5.110.18]) by int-mx12.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id q95BQKGD022278 for ; Fri, 5 Oct 2012 07:26:20 -0400 Received: from qmta11.emeryville.ca.mail.comcast.net (qmta11.emeryville.ca.mail.comcast.net [76.96.27.211]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id q95BQJrT005140 for ; Fri, 5 Oct 2012 07:26:19 -0400 Message-ID: <506EC2AC.8090505@mohawksoft.com> Date: Fri, 05 Oct 2012 07:21:16 -0400 From: Mark Woodward MIME-Version: 1.0 References: <506C5CD8.2070502@mohawksoft.com> <506CFA0B.4000006@tlinx.org> <506D055E.901@mohawksoft.com> <506D1931.4040102@tlinx.org> <506D624A.5070104@mohawksoft.com> <506DA0B4.5020208@redhat.com> <506DA504.8010509@mohawksoft.com> <506EA7C8.409@redhat.com> In-Reply-To: <506EA7C8.409@redhat.com> Content-Transfer-Encoding: 7bit Subject: Re: [linux-lvm] access or interface to list of blocks that have, changed via C.O.W.? Reply-To: LVM general discussion and development List-Id: LVM general discussion and development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , List-Id: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: "Bryn M. Reeves" Cc: Linda Walsh , LVM general discussion and development On 10/05/2012 05:26 AM, Bryn M. Reeves wrote: > On 10/04/2012 04:02 PM, Mark Woodward wrote: >> On 10/04/2012 10:44 AM, Bryn M. Reeves wrote: >>> Really? I'd be surprised if it even builds against modern kernels or >>> device-mapper. >> Well..... >> The LVM2 code that ships with most distros still uses the old interfaces >> and still (Ubuntu 12.04) seemst to create a COW file with SnAp > Yes; that's the traditional dm-snapshot target that has been in the > kernel for years. The Zumastor/ddsnap stuff was a separate project to > replace that using a new metadata format and target - they are not the > same and the Zumastor snapshot code was never merged in the kernel. So, after this discussion, I went to my Ubuntu 12.04 system (3.2.0) and tried some of my LVM2 utilities, and they read the header but found no changes in a snapshot when clearly there had been some. It seems I am wrong, but I'm a little confused, did the developers change the format of the snapshot data COW file without changing the file header signature? If so, that is very bad thing to do. If the COW format has changed and the device header signature has not, how does one correctly determine how the data is stored? > >>> Snapshots using the thinp target use the metadata format described in >>> dm-thin-metadata.c. >> Where are these files to be found? > In drivers/md in the kernel sources - the dm-thin stuff was merged after > 3.1 (October last year); see commits starting with 991d9fa. > > Regards, > Bryn.