From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:45814) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QLj1E-0007sa-Jp for qemu-devel@nongnu.org; Sun, 15 May 2011 17:38:33 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1QLj1D-000617-6C for qemu-devel@nongnu.org; Sun, 15 May 2011 17:38:32 -0400 Received: from qmta03.westchester.pa.hmc1.comcast.net ([76.96.53.20]:57966) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QLj1D-00060m-1F for qemu-devel@nongnu.org; Sun, 15 May 2011 17:38:31 -0400 Message-ID: <4DD047D2.2020201@sundar.org> Date: Sun, 15 May 2011 14:38:26 -0700 From: Jagane Sundar MIME-Version: 1.0 References: <4DC7EEB0.3040007@redhat.com> <4DCBFDB2.6010801@redhat.com> <4DCCA278.1000508@sundar.org> <4DD04231.9010501@redhat.com> In-Reply-To: <4DD04231.9010501@redhat.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [RFC] live snapshot, live merge, live block migration List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "dlaor@redhat.com" Cc: Kevin Wolf , Anthony Liguori , "kvm@vger.kernel.org" , Jes Sorensen , Marcelo Tosatti , qemu-devel , Avi Kivity , Stefan Hajnoczi Hello Dor, > One important advantage of live snapshot over live backup is support of > multiple (consecutive) live snapshots while there can be only a single > live backup at one time. > > This is why I tend to think that although live backup carry some benefit > (no merge required), the live snapshot + live merge are more robust > mechanism. > The two things that concern me regarding the live snapshot/live merge approach are: 1. Performance considerations of having multiple active snapshots? 2. Robustness of this solution in the face of errors in the disk, etc. If any one of the snapshot files were to get corrupted, the whole VM is adversely impacted. The primary goal of Livebackup architecture was to have zero performance impact on the running VM. Livebackup impacts performance of the VM only when the backup client connects to qemu to transfer the modified blocks over, which should be, say 15 minutes a day, for a daily backup schedule VM. One useful thing to do is to evaluate the important use cases for this technology, and then decide which approach makes most sense. As an example, let me state this use case: - A IaaS cloud, where VMs are always on, running off of a local disk, and need to be backed up once a day or so. Can you list some of the other use cases that live snapshot and live merge were designed to solve. Perhaps we can put up a single wiki page that describes all of these proposals. Thanks, Jagane