From mboxrd@z Thu Jan 1 00:00:00 1970 From: Douglas McClendon Subject: Re: DM_snapshot_cow filesystem (dmsetup create snapshot) Date: Wed, 30 Nov 2011 17:34:25 -0600 Message-ID: <4ED6BD81.4090609@filteredperception.org> References: <4EABE131.8010706@googlemail.com> <20111029204947.GU23336@agk-dp.fab.redhat.com> <4ED2DF0F.1070108@filteredperception.org> <4ED59040.50406@filteredperception.org> <20111130220259.GA7595@agk-dp.fab.redhat.com> Reply-To: device-mapper development Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20111130220259.GA7595@agk-dp.fab.redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com To: dm-devel@redhat.com List-Id: dm-devel.ids On 11/30/2011 04:03 PM, Alasdair G Kergon wrote: > On Wed, Nov 30, 2011 at 04:48:05PM -0500, Frederick Grose wrote: >> snapshot Invalid does seem to prevent even read-only access. > > Indeed - once it's invalid, that's the end of it. > If we didn't do that, changes to areas of the origin that hadn't already > changed would start to appear in the 'snapshot' and the snapshot would become a > nonsensical hybrid of the two devices containing no information about which > parts of it got corrupted. > > Don't allow your snapshots to run out of space! So wouldn't it be much better as far as the user is concerned if, the instant a snapshot reached capacity, it fell over into a read-only state (instead of being marked invalid?), such that further corruption beyond such plug-pulling variety could/would not occur? If so, would it be straightforward to write such a patch and would it be beneficial enough to end upstream? -dmc > If you want to see what you can recover, use that code I mentioned earlier. > > Alasdair > > -- > dm-devel mailing list > dm-devel@redhat.com > https://www.redhat.com/mailman/listinfo/dm-devel