From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:60444) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QXrcg-0002UP-Je for qemu-devel@nongnu.org; Sat, 18 Jun 2011 05:15:28 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1QXrcb-0000TN-4s for qemu-devel@nongnu.org; Sat, 18 Jun 2011 05:15:22 -0400 Received: from mail-gw0-f45.google.com ([74.125.83.45]:47591) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QXrcb-0000TI-2U for qemu-devel@nongnu.org; Sat, 18 Jun 2011 05:15:17 -0400 Received: by gwb19 with SMTP id 19so140784gwb.4 for ; Sat, 18 Jun 2011 02:15:16 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20110617123152.GA7379@amt.cnet> References: <1308075511-4745-1-git-send-email-stefanha@linux.vnet.ibm.com> <4DF9F899.5050301@redhat.com> <4DF9FBE4.9080300@redhat.com> <4DFA004E.9010001@redhat.com> <20110616145243.GB12173@amt.cnet> <20110616153018.GA20714@stefanha-thinkpad.localdomain> <20110617123152.GA7379@amt.cnet> Date: Sat, 18 Jun 2011 10:15:15 +0100 Message-ID: From: Stefan Hajnoczi Content-Type: text/plain; charset=ISO-8859-1 Subject: Re: [Qemu-devel] Image streaming and live block copy List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Marcelo Tosatti Cc: Kevin Wolf , Anthony Liguori , Stefan Hajnoczi , jes sorensen , Dor Laor , qemu-devel@nongnu.org, Avi Kivity , Adam Litke On Fri, Jun 17, 2011 at 1:31 PM, Marcelo Tosatti wrote: > On Thu, Jun 16, 2011 at 04:30:18PM +0100, Stefan Hajnoczi wrote: >> On Thu, Jun 16, 2011 at 11:52:43AM -0300, Marcelo Tosatti wrote: >> This approach does not use the backing file feature? >> >> > blkstream block driver: >> > >> > - Maintain in memory whether given block is allocated in local image, >> > if not, read from remote, write to local. Set block as local. >> > Local and remote simply two block drivers from image streaming driver >> > POV. >> > - Once all blocks are local, notify mgmt so it can switch to local >> > copy. >> > - Writes are mirrored to source and destination, minding guest writes >> > over copy writes. >> >> We open the remote file read-only for image streaming and do not want to >> mirror writes. > > Why not? Is there any disadvantage of mirroring writes? Think of the use case with a Fedora master image over NFS. You want a local clone of that master image and use the stream command to copy the data from the master image into the local clone. You cannot modify that master image because other VMs are using it too and/or you want to be able to clone new VMs from it in the future. Stefan