Thank Stefan,that's clear now.
Maybe one more question, about qemu snapshot that I don't understand. I work since many years with snapshot on zfs or netapp, and on these system like ceph, I can rollback at the time of the snapshot, and have a view of when the snapshot was taken. exemple : image1 : empty dir / take a snapshot (snap1) touch /file1 now rollback to snap1 ls / ->empty dir, like when snap1 was taken now,example with qemu: image1 : empty dir / take a snapshot: (qemu-img snapshot -c snap1 image1) touch /file1 now rollback to snap1 (qemu-img snapshot -a snap1 image1) ls /file1 the behaviour is completly different. Did I miss something ? ----- Mail original ----- De: "Stefan Hajnoczi" <stefa...@gmail.com> À: "Alexandre DERUMIER" <aderum...@odiso.com> Cc: "Jeff Cody" <jc...@redhat.com>, "qemu-devel" <qemu-devel@nongnu.org> Envoyé: Samedi 25 Août 2012 16:01:45 Objet: Re: [Qemu-devel] qcow2: online snasphots : internal vs external ? On Sat, Aug 25, 2012 at 2:25 PM, Alexandre DERUMIER <aderum...@odiso.com> wrote: > I'm currently looking to add live snapshot support to proxmox kvm > distribution. > > Is it possible to use internal snapshots on a running guest running qcow2 > disk? > (qemu-img snapshot -c ) ? No. qemu-img should not be used if the guest is running. > Or do I need to use external snapshots with qmp blockdev-snapshot-sync ? > (Seem more complex to delete old snapshots) External qcow2/qed snapshots can be created while the guest is running using snapshot-blockdev-sync, but it is not yet possible to flatten the chain arbitrarily while the guest is running. You can use block-stream to populate the top-most image file with data from its backing image chain. Jeff Cody is working on block-commit which allows merging down (this is the opposite of block-stream). The advantage with block-commit is that backing images are often smaller than the image file, it's therefore more efficient to copy less data down instead of copying the backing image up into the image file. Stefan -- -- Alexandre D e rumier Ingénieur Systèmes et Réseaux Fixe : 03 20 68 88 85 Fax : 03 20 68 90 88 45 Bvd du Général Leclerc 59100 Roubaix 12 rue Marivaux 75002 Paris
