From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:52998) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1T6H4k-0001VX-21 for qemu-devel@nongnu.org; Tue, 28 Aug 2012 04:23:13 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1T6H4d-00080n-WE for qemu-devel@nongnu.org; Tue, 28 Aug 2012 04:23:06 -0400 Received: from mailpro.odiso.net ([89.248.209.98]:39105) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1T6H4d-00080W-Ml for qemu-devel@nongnu.org; Tue, 28 Aug 2012 04:22:59 -0400 Date: Tue, 28 Aug 2012 10:22:34 +0200 (CEST) From: Alexandre DERUMIER Message-ID: <41bcd2dc-b0f2-4843-8c38-bc6d3fb2d957@mailpro> In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Subject: Re: [Qemu-devel] qcow2: online snasphots : internal vs external ? List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Stefan Hajnoczi Cc: Kevin Wolf , Jeff Cody , qemu-devel , "pve-devel@pve.proxmox.com" , Paolo Bonzini , Eric Blake > However, if a disk-only snapshot is enough (this is what qemu-img > snapshot -c would produce), it would be a trivial patch to add a savevm > option to omit the VM state - and even though the snapshot is then still = > not really performed in the background, it should be quick enough to be > workable. I found a old patch RFC from 2010 for savevm to omit the vmstate http://lists.nongnu.org/archive/html/qemu-devel/2010-09/msg00655.html >>The change to qmp-transaction or snapshot-blkdev-sync should be >>similarly small. I think savevm/loadvm isn't the right place to add >>disk-only snapshots since we already have >>qmp-transaction/snapshot-blkdev-sync for that. But indeed, qmp-transaction/snapshot-blkdev-sync seem to be better place. ----- Mail original ----- De: "Stefan Hajnoczi" =C3=80: "Kevin Wolf" Cc: "Alexandre DERUMIER" , "Paolo Bonzini" , "Jeff Cody" , "Eric Blake" , "qemu-devel" Envoy=C3=A9: Mardi 28 Ao=C3=BBt 2012 10:11:18 Objet: Re: [Qemu-devel] qcow2: online snasphots : internal vs external ? On Mon, Aug 27, 2012 at 5:12 PM, Kevin Wolf wrote: > Am 27.08.2012 11:04, schrieb Stefan Hajnoczi: >> On Sun, Aug 26, 2012 at 10:56 AM, Alexandre DERUMIER >> wrote: >>> It is possible to achieve the same behaviour with external snapshot ? (= I would like to do it online) >>> I don't see how I can rollback to the point of time of the snapshot. >> >> The snapshot only captures the contents of the disk. Rollback does >> not make sense without shutting down the guest. The OS/file system >> would be very confused if the disk contents changed underneath it. >> >> Existing hotplug can be used. For example, if we have an external >> snapshot of a virtio-blk drive, we can use hotplug to remove the >> drive, choose the snapshot file and attach it again. This only works >> for "data" drives, the root file system usually cannot be changed >> while the guest is running. >> >> You may also wish to look at libvirt for higher level snapshot primitive= s. >> >>> Also I see that snapshot_blkdev qmp command give in his description: >>> "Otherwise the snapshot will be internal! (currently unsupported)." >>> >>> is Live internal snapshots on the roadmap ? >> >> I'm not aware of anyone working on adding internal snapshot in the >> near future. Patches are welcome. > > I wonder why nobody mentioned the savevm/loadvm monitor commands, which > do take an internal snapshot of a running VM. They just aren't live, and = > when writing out the whole VM state this matters indeed. > > However, if a disk-only snapshot is enough (this is what qemu-img > snapshot -c would produce), it would be a trivial patch to add a savevm > option to omit the VM state - and even though the snapshot is then still = > not really performed in the background, it should be quick enough to be > workable. The change to qmp-transaction or snapshot-blkdev-sync should be similarly small. I think savevm/loadvm isn't the right place to add disk-only snapshots since we already have qmp-transaction/snapshot-blkdev-sync for that. Stefan -- -- Alexandre D e rumier Ing=C3=A9nieur Syst=C3=A8mes et R=C3=A9seaux Fixe : 03 20 68 88 85 Fax : 03 20 68 90 88 45 Bvd du G=C3=A9n=C3=A9ral Leclerc 59100 Roubaix 12 rue Marivaux 75002 Paris