From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marcelo Tosatti Subject: Re: [Qemu-devel] KVM call agenda for June 28 Date: Tue, 5 Jul 2011 09:58:58 -0300 Message-ID: <20110705125858.GA21254@amt.cnet> References: <20110628194106.GA17443@amt.cnet> <4E0ADAE0.6040204@redhat.com> <20110629154134.GA6631@amt.cnet> <20110630143620.GA4366@amt.cnet> <4E0C8D90.8050305@redhat.com> <20110630183829.GA8752@amt.cnet> <4E12C4F5.9000100@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: dlaor@redhat.com, Kevin Wolf , Chris Wright , KVM devel mailing list , quintela@redhat.com, qemu-devel@nongnu.org, Avi Kivity , jes sorensen To: Stefan Hajnoczi Return-path: Received: from mx1.redhat.com ([209.132.183.28]:48671 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756120Ab1GEM7O (ORCPT ); Tue, 5 Jul 2011 08:59:14 -0400 Content-Disposition: inline In-Reply-To: Sender: kvm-owner@vger.kernel.org List-ID: On Tue, Jul 05, 2011 at 01:40:08PM +0100, Stefan Hajnoczi wrote: > On Tue, Jul 5, 2011 at 9:01 AM, Dor Laor wrote: > > I tried to re-arrange all of the requirements and use cases using this wiki > > page: http://wiki.qemu.org/Features/LiveBlockMigration > > > > It would be the best to agree upon the most interesting use cases (while we > > make sure we cover future ones) and agree to them. > > The next step is to set the interface for all the various verbs since the > > implementation seems to be converging. > > Live block copy was supposed to support snapshot merge. I think the > current favored approach is to make the source image a backing file to > the destination image and essentially do image streaming. > > Using this mechanism for snapshot merge is tricky. The COW file > already uses the read-only snapshot base image. So now we cannot > trivally copy the COW file contents back into the snapshot base image > using live block copy. It never did. Live copy creates a new image were both snapshot and "current" are copied to. This is similar with image streaming. > It seems like snapshot merge will require dedicated code that reads > the allocated clusters from the COW file and writes them back into the > base image. > > A very inefficient alternative would be to create a third image, the > "merge" image file, which has the COW file as its backing file: > snapshot (base) -> cow -> merge > > All data from snapshot and cow is copied into merge and then snapshot > and cow can be deleted. But this approach is results in full data > copying and uses potentially 3x space if cow is close to the size of > snapshot. Management can set a higher limit on the size of data that is merged, and create a new base once exceeded. This avoids copying excessive amounts of data. > Any other ideas that reuse live block copy for snapshot merge? > > Stefan From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:51952) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Qe5Dh-0003xa-0m for qemu-devel@nongnu.org; Tue, 05 Jul 2011 08:59:18 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Qe5De-00018S-ON for qemu-devel@nongnu.org; Tue, 05 Jul 2011 08:59:16 -0400 Received: from mx1.redhat.com ([209.132.183.28]:24656) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Qe5De-000188-2q for qemu-devel@nongnu.org; Tue, 05 Jul 2011 08:59:14 -0400 Date: Tue, 5 Jul 2011 09:58:58 -0300 From: Marcelo Tosatti Message-ID: <20110705125858.GA21254@amt.cnet> References: <20110628194106.GA17443@amt.cnet> <4E0ADAE0.6040204@redhat.com> <20110629154134.GA6631@amt.cnet> <20110630143620.GA4366@amt.cnet> <4E0C8D90.8050305@redhat.com> <20110630183829.GA8752@amt.cnet> <4E12C4F5.9000100@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Subject: Re: [Qemu-devel] KVM call agenda for June 28 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Stefan Hajnoczi Cc: Kevin Wolf , Chris Wright , KVM devel mailing list , quintela@redhat.com, jes sorensen , dlaor@redhat.com, qemu-devel@nongnu.org, Avi Kivity On Tue, Jul 05, 2011 at 01:40:08PM +0100, Stefan Hajnoczi wrote: > On Tue, Jul 5, 2011 at 9:01 AM, Dor Laor wrote: > > I tried to re-arrange all of the requirements and use cases using this wiki > > page: http://wiki.qemu.org/Features/LiveBlockMigration > > > > It would be the best to agree upon the most interesting use cases (while we > > make sure we cover future ones) and agree to them. > > The next step is to set the interface for all the various verbs since the > > implementation seems to be converging. > > Live block copy was supposed to support snapshot merge. I think the > current favored approach is to make the source image a backing file to > the destination image and essentially do image streaming. > > Using this mechanism for snapshot merge is tricky. The COW file > already uses the read-only snapshot base image. So now we cannot > trivally copy the COW file contents back into the snapshot base image > using live block copy. It never did. Live copy creates a new image were both snapshot and "current" are copied to. This is similar with image streaming. > It seems like snapshot merge will require dedicated code that reads > the allocated clusters from the COW file and writes them back into the > base image. > > A very inefficient alternative would be to create a third image, the > "merge" image file, which has the COW file as its backing file: > snapshot (base) -> cow -> merge > > All data from snapshot and cow is copied into merge and then snapshot > and cow can be deleted. But this approach is results in full data > copying and uses potentially 3x space if cow is close to the size of > snapshot. Management can set a higher limit on the size of data that is merged, and create a new base once exceeded. This avoids copying excessive amounts of data. > Any other ideas that reuse live block copy for snapshot merge? > > Stefan