From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Dr. David Alan Gilbert" Subject: Re: [Qemu-devel] [RFC]VM live snapshot proposal Date: Tue, 4 Mar 2014 09:40:32 +0000 Message-ID: <20140304094031.GC2711@work-vm> References: <615092B2FD0E7648B6E4B43E029BCFB84D578044@SZXEMA503-MBS.china.huawei.com> <20140303123234.GC21055@stefanha-thinkpad.redhat.com> <20140303125520.GF4850@dhcp-200-207.str.redhat.com> <53148169.6060700@redhat.com> <20140303133034.GI4850@dhcp-200-207.str.redhat.com> <615092B2FD0E7648B6E4B43E029BCFB84D57953F@SZXEMA503-MBS.china.huawei.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Kevin Wolf , Paolo Bonzini , Pavel Hrdina , Zhanghailiang , KVM devel mailing list , Stefan Hajnoczi , "qemu-devel@nongnu.org" , Wenchao Xia To: "Huangpeng (Peter)" Return-path: Received: from mx1.redhat.com ([209.132.183.28]:50842 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756631AbaCDJko (ORCPT ); Tue, 4 Mar 2014 04:40:44 -0500 Content-Disposition: inline In-Reply-To: <615092B2FD0E7648B6E4B43E029BCFB84D57953F@SZXEMA503-MBS.china.huawei.com> Sender: kvm-owner@vger.kernel.org List-ID: * Huangpeng (Peter) (peter.huangpeng@huawei.com) wrote: > > > I think this is different in the same way that block-backup and > > > block-mirror are different. Huangpeng's proposal would let you make a > > > consistent snapshot of disks and RAM. > > > > Right. Though the point isn't about consistency (doing the disk snapshot when > > memory has converged would be consistent as well), but about having the > > snapshot semantically right at the time when the monitor command is issued > > instead of only starting it then and being consistent at the point of completion. > > > > This is indeed like pre/post-copy live migration, and probably both options have > > their uses. I would suggest starting with the easy one, and adding the > > post-copy feature on top. > > > > Good suggestion, The latest patches of post-copy seems updated 2 years ago. > https://github.com/yamahata/qemu I'm working on post-copy at the moment, using Andrea's kernel code, using bits of Yamahata's code base as well; hopefully it won't be too long until we have something to post. > One question: > Can post-copy fallback if exceptions happen during post-copy? What do you mean by 'exceptions' here? Generally postcopy can't fall back to precopy because once you're in postcopy mode the state is split between the two machines. Dave -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK