From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tomasz Chmielewski Subject: Re: making snapshots with raw devices? and some general snapshot thoughts Date: Wed, 25 Feb 2009 15:31:02 +0100 Message-ID: <49A55626.3020009@wpkg.org> References: <49A545AA.60508@wpkg.org> <90eb1dc70902250610l68ea11a4y6aab86ac4611dc25@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: "kvm@vger.kernel.org" To: Javier Guerra Return-path: Received: from mx03.syneticon.net ([78.111.66.105]:38707 "EHLO mx03.syneticon.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754742AbZBYOai (ORCPT ); Wed, 25 Feb 2009 09:30:38 -0500 In-Reply-To: <90eb1dc70902250610l68ea11a4y6aab86ac4611dc25@mail.gmail.com> Sender: kvm-owner@vger.kernel.org List-ID: Javier Guerra schrieb: > On Wed, Feb 25, 2009 at 8:20 AM, Tomasz Chmielewski wrote: >> Is it possible to make snapshots when using raw devices (i.e. disk, >> partition, LVM volume) as guest's disk image? >> >> According to documentation[1] (and some tests I made) it is only possible >> with qcow2 images. Which makes it very inflexible: >> >> - one is forced to use a potentially slower file access >> - one can't use the benefits of i.e. iSCSI disk access, SAN etc. > > what about using 'good' block devices, and add one small, mostly empty > qcow2? could it be used to store the snapshot for all? of course it > would degrade performance while it's active, but should revert after > 'commiting' it to the 'real' block device(s) It doesn't work for me - I get: qm> savevm 1 Error while creating snapshot on 'virtio0' Where "virtio0" is my "real" block device. I guess it still wants to write a snapshot there, as outlined in the documentation: "The VM state info is stored in the first qcow2 non removable and writable block device. The disk image snapshots are stored in every disk image." Or, am I making a mistake here? Besides: - guest will see this second device - not needed - still, we save the state of disks, but we don't need it for tasks like "pausing guest, upgrading kernel on host, rebooting host, resuming guest" -- Tomasz Chmielewski http://wpkg.org