On Tue, Jan 30, 2018 at 01:17:21PM +0100, Gionatan Danti wrote:
> Hi all,
> on a fully patched CentOS 7.4 x86-64, I see the following behavior:
>
> - when creating a new volumes using vol-create-as, the resulting file is a
> qcow2 version 2 (compat=0.10) file. Example:
>
> [root@gdanti-lenovo vmimages]# virsh vol-create-as default zzz.qcow2
> 8589934592 --format=qcow2 --backing-vol /mnt/vmimages/centos6.img
> Vol zzz.qcow2 created
Yes, for sake of backcompat we default to v2 unless something
requires v3. You can't use vol-create-as to create a v3 image,
you need to use the XML input.
Either force the use of v3:
<volume>
<name>demo.qcow2</name>
<capacity>1073741824</capacity>
<target>
<format type='qcow2'/>
<compat>1.1</compat>
</target>
</volume>
Or request some feature that implies v3:
<volume>
<name>demo.qcow2</name>
<capacity>1073741824</capacity>
<target>
<format type='qcow2'/>
<features>
<lazy_refcounts/>
</features>
</target>
</volume>
and pass this XML to virsh vol-create
> It is possible to create a new volume using qcow2 version 3 (compat=1.1)
> format *using libvirt/virsh* (I know I can do that via qemu-img)? Any
> drawback on using version 3 format?
The only drawback is OS compatibility.
Regards,
Daniel
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