From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1LaYXF-000857-C8 for qemu-devel@nongnu.org; Fri, 20 Feb 2009 11:47:33 -0500 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1LaYXC-00084v-Uf for qemu-devel@nongnu.org; Fri, 20 Feb 2009 11:47:32 -0500 Received: from [199.232.76.173] (port=55667 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1LaYXC-00084s-Ol for qemu-devel@nongnu.org; Fri, 20 Feb 2009 11:47:30 -0500 Received: from mx20.gnu.org ([199.232.41.8]:35034) by monty-python.gnu.org with esmtps (TLS-1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.60) (envelope-from ) id 1LaYXC-0006m5-CM for qemu-devel@nongnu.org; Fri, 20 Feb 2009 11:47:30 -0500 Received: from mail.codesourcery.com ([65.74.133.4]) by mx20.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1LaYXB-0006Kn-Ef for qemu-devel@nongnu.org; Fri, 20 Feb 2009 11:47:29 -0500 From: Paul Brook Subject: Re: [Qemu-devel] [RFC] More robust migration Date: Fri, 20 Feb 2009 16:47:26 +0000 References: <499EBFD8.50307@amd.com> <200902201609.11547.paul@codesourcery.com> <20090220163820.GC9726@shareable.org> In-Reply-To: <20090220163820.GC9726@shareable.org> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200902201647.27138.paul@codesourcery.com> Reply-To: qemu-devel@nongnu.org List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org On Friday 20 February 2009, Jamie Lokier wrote: > Paul Brook wrote: > > I suspect that in practice live migration of a VM between different qemu > > versions ends up comparable to in-place live kernel upgrades. i.e. it > > takes an awful lot of work and care to make it happen, and in practice > > isn't going to happen for any particularly useful span of versions. > > On the other hand, stored snapshots of guests which are ready to run > in a particular state are quite useful. I'm under the impression the > migration code is/will be useful for storing snapshots of system (not > disk) state too. Is that right? I don't think there's any real difference between snapshotting and migration in this case. It's basically the same code. I'm not saying it's a useless feature, just that it's very extremely to do reliably, and for that reason unlikely to happen. An unreliable implementation (i.e. one that claims to migrate/snapshot, then breaks some of the time) is IMHO worse than nothing. Paul