From: Anthony Liguori Subject: Re: [Qemu-devel] qemu-img commit -- is there a limit on file sizes? Date: Mon, 01 Dec 2008 11:14:08 -0600 Message-ID: <49341B60.3090306@codemonkey.ws> References: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: kvm-devel , Avi Kivity To: qemu-devel@nongnu.org Return-path: Received: from mail-qy0-f11.google.com ([209.85.221.11]:42398 "EHLO mail-qy0-f11.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751275AbYLARON (ORCPT ); Mon, 1 Dec 2008 12:14:13 -0500 Received: by qyk4 with SMTP id 4so2763714qyk.13 for ; Mon, 01 Dec 2008 09:14:11 -0800 (PST) In-Reply-To: Sender: kvm-owner@vger.kernel.org List-ID: walt wrote: > Some background for my question: I've been trying to install > and then update Windows Vista using kvm. Everything works great > until I use 'qemu-img commit' to apply all the Windows Updates > to my original base install of Vista. > > After doing the qemu-img commit step, the backing file is now > corrupt, 100% reproducibly. I don't have the same problem with > Windows XP, however, and I wondered if the problem is caused by > the sheer size of the commit that Vista requires. > > When I install XP, then windows-update, and then qemu-img commit > the updates, I'm committing about 1GB of updates to a 3GB backing > file. > > When I install Vista and then later commit the Vista updates, I'm > committing a 3GB file to a 6GB backing file, and that's when the > corruption happens every time. > > So I tried an experiment with Vista -- I deliberately limit the > number of windows updates I allow at any one time, and then use > qemu-img commit after each small update. Voila, everything now > works perfectly -- no file corruption! We've started getting some reports of corruption on "commit" in KVM. There is a long standing disk corruption issue too that is very difficult to reproduce. The thinking is that there is a bug somewhere in the qcow2 code. Is anyone actively looking into this? Regards, Anthony Liguori > And that's why I suspect there is a functional limit to the size > of each commit I can do with qemu-img. > > Any thoughts or possible diagnostic maneuvers to be tried? > > Thanks! > > (BTW, I get the same results using 32-bit linux and 64-bit linux > on the same amd64 machine, using both gcc3 and gcc4.) > > >