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Re: [Qemu-devel] using "qemu-img convert -O qcow2" to convert qcow v1 to

From: Eric Blake
Subject: Re: [Qemu-devel] using "qemu-img convert -O qcow2" to convert qcow v1 to v2 creates a qcow v3 file?
Date: Mon, 13 Nov 2017 11:55:13 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0

On 11/13/2017 11:14 AM, Peter Maydell wrote:> I have a qcow v1 file
which I created by mistake (forgetting that
> you need to tell qemu-img create 'qcow2' and not just 'qcow'),
> which I want to convert to a v2 file so I can put snapshots into
> it. But when I try to do this with qemu-img convert it creates a
> v3 file instead:
> $ file hda-old.qcow
> hda-old.qcow: QEMU QCOW Image (v1), 5368709120 bytes
> $ build/x86/qemu-img convert -O qcow2 hda-old.qcow hda.qcow2
> $ file hda.qcow2
> hda.qcow2: QEMU QCOW Image (v3), 5368709120 bytes
> and if you then try to use that in QEMU it complains:
> qemu-system-aarch64: -drive if=none,file=hda.qcow2,format=qcow,id=hd:
> Unsupported qcow version 3
> What am I missing here?
qcow2 has two versions; v2 (aka compat=0.10), and v3 (aka compat=1.1).
We changed qemu-img to create v3 by default several years ago, but there
are older qemu binaries (hello, CentOS 6) that still don't understand
v3.  Your qemu-system-aarch64 appears to be one of these older binaries.

qemu-img convert -O qcow2 -o compat=0.10 hda-old.qcow hda.qcow2

Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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