[libvirt-users] Create qcow2 v3 volumes via libvirt

[Daniel P. Berrangé]

On Tue, May 01, 2018 at 12:35:05PM +0200, Gianluca Cecchi wrote:
> On Tue, May 1, 2018 at 10:45 AM, Daniel P. Berrangé <berrange at redhat.com>
> wrote:
> 
> > 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 at 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.
> >
> 
> 
> BTW: in virt-manager of CentOS 7.4 by default qcow2 disks (see below for
> zzz3.qcow2) are created with compatibility 1.1 (probably indirectly because
> of its lazy refcounts feature enabled, as Daniel wrote):

Yes, virt-manager explicitly turns on lazy refcounts if it sees a new
enough QEMU, so will get v3


Regards,
Daniel
-- 
|: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
|: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|