Il 30-01-2018 13:17 Gionatan Danti ha scritto:
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.
Hi all, anyone with some thoughts on the matter? Another question: how reliable are qcow2 ver2/3 files nowadays? Are you using them in production environments? At the moment, I am using RAW files and filesystem-level snapshot to manage versioning; however, as virt-manager has direct support for managing qcow2 internal snapshots, it would be easier to deploy qcow2 disks. What strikes me is that, if thing have not changed, Red Hat support policy was to *not* support internal snapshots. So, are they reliable enough for production VMs? Thanks. -- Danti Gionatan Supporto Tecnico Assyoma S.r.l. - www.assyoma.it email: g.danti@assyoma.it - info@assyoma.it GPG public key ID: FF5F32A8