From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=39017 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1OoGAm-0001Xh-JI for qemu-devel@nongnu.org; Wed, 25 Aug 2010 09:37:49 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1OoGAl-0000m2-3P for qemu-devel@nongnu.org; Wed, 25 Aug 2010 09:37:48 -0400 Received: from mail-qy0-f180.google.com ([209.85.216.180]:52700) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1OoGAl-0000lr-1H for qemu-devel@nongnu.org; Wed, 25 Aug 2010 09:37:47 -0400 Received: by qyk31 with SMTP id 31so565596qyk.4 for ; Wed, 25 Aug 2010 06:37:46 -0700 (PDT) Message-ID: <4C751CA9.4090200@codemonkey.ws> Date: Wed, 25 Aug 2010 08:37:45 -0500 From: Anthony Liguori MIME-Version: 1.0 References: <1282646430-5777-1-git-send-email-kwolf@redhat.com> <4C73C2BF.8050300@codemonkey.ws> <4C73C622.7080808@redhat.com> <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> <4C7515AE.9020808@redhat.com> In-Reply-To: <4C7515AE.9020808@redhat.com> 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: Avi Kivity Cc: Kevin Wolf , stefanha@gmail.com, mjt@tls.msk.ru, qemu-devel@nongnu.org, hch@lst.de On 08/25/2010 08:07 AM, Avi Kivity wrote: >> >>> The next allocation can then be filled from memory, so the >>> allocation sync is amortized over many blocks. A power fail will >>> leak the preallocated blocks, losing some megabytes of address >>> space, but not real disk space. >> >> It's a clever idea, but it would lose real disk space which is >> probably not a huge issue. > > Not real disk space since no pwrite() would ever touch the disk. If > the image were copied, _then_ we'd lose the disk space, if the copy > command and filesystem don't optimize zeros away. \ Ok. Regards, Anthony Liguori >>>> >>>> And that's it. There is no scenario where the disk is corrupted. >>> >>> _if_ that's the only failure mode. >> >> If we had another disk format that only supported growth and metadata >> for a backing file, can you think of another failure scenario? >> > > I can't think of one, but that's not saying much. >