From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:51894) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XgERN-0001mN-7k for qemu-devel@nongnu.org; Mon, 20 Oct 2014 11:00:15 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1XgERG-0005ji-PF for qemu-devel@nongnu.org; Mon, 20 Oct 2014 11:00:09 -0400 Received: from mx1.redhat.com ([209.132.183.28]:51400) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XgERG-0005ip-Ga for qemu-devel@nongnu.org; Mon, 20 Oct 2014 11:00:02 -0400 Received: from int-mx13.intmail.prod.int.phx2.redhat.com (int-mx13.intmail.prod.int.phx2.redhat.com [10.5.11.26]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id s9KF01DU026228 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL) for ; Mon, 20 Oct 2014 11:00:01 -0400 Date: Mon, 20 Oct 2014 15:59:57 +0100 From: "Dr. David Alan Gilbert" Message-ID: <20141020145956.GL2517@work-vm> References: <1413359710-2799-1-git-send-email-quintela@redhat.com> <543E8B45.3040809@redhat.com> <877g01fhob.fsf@elfo.elfo> <54411C74.2010407@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <54411C74.2010407@redhat.com> Subject: Re: [Qemu-devel] [RFC 0/7] Optional toplevel sections List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paolo Bonzini Cc: kwolf@redhat.com, quintela@redhat.com, qemu-devel@nongnu.org, lcapitulino@redhat.com, laine@redhat.com * Paolo Bonzini (pbonzini@redhat.com) wrote: > Il 15/10/2014 17:59, Juan Quintela ha scritto: > > My idea here is that, if you don't use libvirt, you just start without > > -S. > > If you don't use libvirt or any other QEMU management layer, you're not > going to do migration except for debugging purposes. There's just too > much state going on to be able to do it reliably. I'm not sure that's entirely true - while I agree that most users will use libvirt, migration with shared disk is pretty easy; the only thing that you need to do is bring up the tap on the destination, and I'm not sure libvirt gets the timing ideal for it. Dave > > > If you use libvirt, and you *don't* need to do anything special to run > > after migration, you shouldn't use -S. > > Is this a real requirement, or just "it sounds nicer that way"? How > much time really passes between the end of migration and the issuing of > the "-cont" command? > > And the $1,000,000 questionL.aAre you _absolutely_ sure that an > automatic restart is entirely robust against a failure of the connection > between the two libvirtd instances? Could you end up with the VM > running on two hosts? Using -S gets QEMU completely out of the > equation, which is nice. > > By the way, some of the states (I can think of io-error, guest-panicked, > watchdog) can be detected on the destination and restored. Migrating a > machine with io-error state is definitely something that you want to do > no matter what versions of QEMU you have. It may be the only way to > recover for a network partition like this: > > DISK > / \ > | \ > X | > | | > SRC --- DEST > > (not impossible: e.g. the SRC->DISK is fibre channel, but the SRC->DEST > link is Ethernet. Or you have a replicated disk setup, some daemon > fails in SRC's replica but not DEST's). > > > And I would emit an event saying > > "migration was finished". > > The event should be emitted nevertheless. :) > > Paolo > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK