From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=51728 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1OoGvX-0001je-Ow for qemu-devel@nongnu.org; Wed, 25 Aug 2010 10:26:08 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1OoGvW-00017Y-5l for qemu-devel@nongnu.org; Wed, 25 Aug 2010 10:26:07 -0400 Received: from mail-qy0-f173.google.com ([209.85.216.173]:60171) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1OoGvW-00017S-0j for qemu-devel@nongnu.org; Wed, 25 Aug 2010 10:26:06 -0400 Received: by qyk5 with SMTP id 5so5163099qyk.4 for ; Wed, 25 Aug 2010 07:26:05 -0700 (PDT) Message-ID: <4C7527FC.8030501@codemonkey.ws> Date: Wed, 25 Aug 2010 09:26:04 -0500 From: Anthony Liguori MIME-Version: 1.0 References: <4C73C926.3010901@codemonkey.ws> <4C73C9CF.7090800@redhat.com> <4C73CAA9.2060104@codemonkey.ws> <4C73CB85.9010306@redhat.com> <4C73CBD6.7000900@codemonkey.ws> <4C73CCCB.6050704@redhat.com> <4C73CF8D.5060405@codemonkey.ws> <4C74C2F3.9050506@redhat.com> <4C7510C1.8080305@codemonkey.ws> <4C75195A.8050508@redhat.com> <20100825141830.GA31307@lst.de> In-Reply-To: <20100825141830.GA31307@lst.de> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Subject: [Qemu-devel] Re: [RFC][STABLE 0.13] Revert "qcow2: Use bdrv_(p)write_sync for metadata writes" List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Christoph Hellwig Cc: Kevin Wolf , stefanha@gmail.com, mjt@tls.msk.ru, Avi Kivity , qemu-devel@nongnu.org On 08/25/2010 09:18 AM, Christoph Hellwig wrote: > On Wed, Aug 25, 2010 at 04:23:38PM +0300, Avi Kivity wrote: > >> On 08/25/2010 03:46 PM, Anthony Liguori wrote: >> >>> If we had another disk format that only supported growth and metadata >>> for a backing file, can you think of another failure scenario? >>> >> btw, only supporting growth is a step backwards. Currently file-backed >> disks keep growing even the guest-used storage doesn't grow, since once >> we allocate something we never release it. But eventually guests will >> start using TRIM or DISCARD or however it's called, and then we can >> expose it and reclaim unused blocks. >> > Together with file level snapshots Thin Provisioning support basically > makes qcow2 obsolete. > I think we'll always need a sparse image format. As long as people copy images to USB thumb drives containing vfat file systems or over dumb transports like HTTP, it will be necessary. However, I agree that really advanced things like snapshotting is best done with a smart file system. Regards, Anthony Liguori > I already have a prototype implementation of scsi discard for qemu, > which together with the XFS extent size hints allows us to very > efficiently using growing and shrinking images on the bare filesystem. > XFS at this point doesn't have file-level snapshots, but I'm planning > to port the hole punhing and extent size hints to btrfs and maybe > ocfs2 which will give you all that. > >