Re: [libvirt-users] Create qcow2 v3 volumes via libvirt

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 [root@gdanti-lenovo vmimages]# file zzz.qcow2 zzz.qcow2: QEMU QCOW Image (v2), has backing file (path /mnt/vmimages/centos6.img), 8589934592 bytes [root@gdanti-lenovo vmimages]# qemu-img info zzz.qcow2 image: zzz.qcow2 file format: qcow2 virtual size: 8.0G (8589934592 bytes) disk size: 196K cluster_size: 65536 backing file: /mnt/vmimages/centos6.img backing file format: raw Format specific information: compat: 0.10 refcount bits: 16 - when creating a snapshot, the resulting file is a qcow2 version 3 (comapt=1.1) file. Example: [root@gdanti-lenovo vmimages]# virsh snapshot-create-as centos6left --disk-only --no-metadata snap.qcow2 Domain snapshot snap.qcow2 created [root@gdanti-lenovo vmimages]# file centos6left.snap.qcow2 centos6left.snap.qcow2: QEMU QCOW Image (v3), has backing file (path /mnt/vmimages/centos6left.qcow2), 8589934592 bytes [root@gdanti-lenovo vmimages]# qemu-img info centos6left.snap.qcow2 image: centos6left.snap.qcow2 file format: qcow2 virtual size: 8.0G (8589934592 bytes) disk size: 196K cluster_size: 65536 backing file: /mnt/vmimages/centos6left.qcow2 backing file format: qcow2 Format specific information: compat: 1.1 lazy refcounts: false refcount bits: 16 corrupt: false From what I know, this is a deliberate decision: compat=1.1 requires relatively recent qemu version, and creating a new volume play on the "safe side" of compatibility. 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? Thanks.