Gionatan Danti
2022-Dec-11 19:36 UTC
[Question] Which qcow2 options could be inherited to snapshot/blockcopy?
Il 2022-11-26 10:36 Gionatan Danti ha scritto:> Il 2022-11-21 10:30 Peter Krempa ha scritto: >> In regards to the 'compat' option in terms of snapshots/blockcopy, we >> don't set it and thus use the qemu default. Since both operations >> create >> a new image with an existing qemu instance, the default new qemu >> format >> is okay. > > Hi, some idea on why creating a qcow2 volume and snapshotting it via a > backing file results in two qcow2 files with different format (v2 vs > v3)? Example below: > > # volume creation > [root at whitehole ~]# virsh vol-create-as default zzz.qcow2 1G --format > qcow2 > Vol zzz.qcow2 created > > [root at whitehole ~]# qemu-img info /var/lib/libvirt/images/zzz.qcow2 > image: /var/lib/libvirt/images/zzz.qcow2 > file format: qcow2 > virtual size: 1 GiB (1073741824 bytes) > disk size: 16.5 KiB > cluster_size: 65536 > Format specific information: > compat: 0.10 > compression type: zlib > refcount bits: 16 > > [root at whitehole ~]# file /var/lib/libvirt/images/zzz.qcow2 > /var/lib/libvirt/images/zzz.qcow2: QEMU QCOW2 Image (v2), 1073741824 > bytes > > # snapshot creation > [root at whitehole ~]# virsh snapshot-create-as zzz --name zsnap1 > --disk-only > Domain snapshot zsnap1 created > > [root at whitehole ~]# qemu-img info /var/lib/libvirt/images/zzz.zsnap1 > image: /var/lib/libvirt/images/zzz.zsnap1 > file format: qcow2 > virtual size: 1 GiB (1073741824 bytes) > disk size: 16.5 KiB > cluster_size: 65536 > backing file: /var/lib/libvirt/images/zzz.qcow2 > backing file format: qcow2 > Format specific information: > compat: 1.1 > compression type: zlib > lazy refcounts: false > refcount bits: 16 > corrupt: false > extended l2: false > > [root at whitehole ~]# file /var/lib/libvirt/images/zzz.zsnap1 > /var/lib/libvirt/images/zzz.zsnap1: QEMU QCOW2 Image (v3), has backing > file (path /var/lib/libvirt/images/zzz.qcow2), 1073741824 bytes > > Regards.Hi all, anyone with some ideas/suggestions? Regards. -- Danti Gionatan Supporto Tecnico Assyoma S.r.l. - www.assyoma.it email: g.danti at assyoma.it - info at assyoma.it GPG public key ID: FF5F32A8
Peter Krempa
2022-Dec-12 07:39 UTC
[Question] Which qcow2 options could be inherited to snapshot/blockcopy?
On Sun, Dec 11, 2022 at 20:36:26 +0100, Gionatan Danti wrote:> Il 2022-11-26 10:36 Gionatan Danti ha scritto: > > Il 2022-11-21 10:30 Peter Krempa ha scritto: > > > In regards to the 'compat' option in terms of snapshots/blockcopy, we > > > don't set it and thus use the qemu default. Since both operations > > > create > > > a new image with an existing qemu instance, the default new qemu > > > format > > > is okay. > > > > Hi, some idea on why creating a qcow2 volume and snapshotting it via a > > backing file results in two qcow2 files with different format (v2 vs > > v3)? Example below: > > > > # volume creation > > [root at whitehole ~]# virsh vol-create-as default zzz.qcow2 1G --format > > qcow2 > > Vol zzz.qcow2 created > > > > [root at whitehole ~]# qemu-img info /var/lib/libvirt/images/zzz.qcow2 > > image: /var/lib/libvirt/images/zzz.qcow2 > > file format: qcow2 > > virtual size: 1 GiB (1073741824 bytes) > > disk size: 16.5 KiB > > cluster_size: 65536 > > Format specific information: > > compat: 0.10 > > compression type: zlib > > refcount bits: 16 > > > > [root at whitehole ~]# file /var/lib/libvirt/images/zzz.qcow2 > > /var/lib/libvirt/images/zzz.qcow2: QEMU QCOW2 Image (v2), 1073741824 > > bytes > > > > # snapshot creation > > [root at whitehole ~]# virsh snapshot-create-as zzz --name zsnap1 > > --disk-only > > Domain snapshot zsnap1 created > > > > [root at whitehole ~]# qemu-img info /var/lib/libvirt/images/zzz.zsnap1 > > image: /var/lib/libvirt/images/zzz.zsnap1 > > file format: qcow2 > > virtual size: 1 GiB (1073741824 bytes) > > disk size: 16.5 KiB > > cluster_size: 65536 > > backing file: /var/lib/libvirt/images/zzz.qcow2 > > backing file format: qcow2 > > Format specific information: > > compat: 1.1 > > compression type: zlib > > lazy refcounts: false > > refcount bits: 16 > > corrupt: false > > extended l2: false > > > > [root at whitehole ~]# file /var/lib/libvirt/images/zzz.zsnap1 > > /var/lib/libvirt/images/zzz.zsnap1: QEMU QCOW2 Image (v3), has backing > > file (path /var/lib/libvirt/images/zzz.qcow2), 1073741824 bytes > > > > Regards. > > Hi all, > anyone with some ideas/suggestions?Hi, When creating a snapshot libvirt uses the qemu default for the created qcow2 image's version which is now v3. Do you have any specific use case for keeping them in v2 mode?