Re: [Users] Online snapshot

On 06/28/2012 07:07 AM, Dave Allan wrote: > On Thu, Jun 28, 2012 at 06:34:25AM -0400, Itamar Heim wrote: >> On 06/28/2012 04:40 AM, Winfried de Heiden wrote: >>> Hi all, >>> >>> It seems live snapshot is available in the Fedora 17 qemu-kvm. On my >>> laptop with kvm, virt-manager, libvirt, virsh etc. I created a virtual >>> machine and tried to make a live snapshot: >>> >>> >>> virsh # snapshot-create RHEL55_NTP >>> Domain snapshot 1340871802 created That's a system-checkpoint snapshot, because you didn't use --disk-only. When you say 'live snapshot' were you intending the fast operation of just a disk snapshot (via the 'transaction' or 'blockdev-snapshot-sync' monitor command) or the slow operation of a checkpoint (via the 'savevm' monitor command)? >>> [root@kvm ~]# rpm -qf `which qemu-kvm` >>> qemu-system-x86-1.0-17.fc17.x86_64 >>> >>> [wdh@laptop-winfried ~]$ rpm -qf `which qemu-kvm` >>> qemu-system-x86-1.0-17.fc17.x86_64 This qemu does not support the 'transaction' monitor command, so libvirt has to fall back to the non-atomic 'blockdev-snapshot-sync', or else give up because of missing functionality. >> >> dave - who can help us elaborate on this libvirt error: >> reuse is not supported with >> this QEMU binary >>>> >>>> this is the relevant error coming from libvirt. >>>> maybe fedora 17 qemu-kvm does not have live snapshot support? >>>> >>>> Thread-306::ERROR::2012-06-27 >>>> 12:46:40,178::libvirtvm::1782::vm.Vm::(snapshot) >>>> vmId=`ef978066-09c8-40aa-8e0b-4accfacc15bd`::Unable to take snapshot >>>> Traceback (most recent call last): >>>> File "/usr/share/vdsm/libvirtvm.py", line 1780, in snapshot >>>> libvirt.VIR_DOMAIN_SNAPSHOT_CREATE_REUSE_EXT)) OK, so this is a case of VDSM driving a different use of the API than what you did with your virsh command line. VDSM is attempting to do the equivalent of 'virsh snapshot-create --disk-only --reuse-ext', but because your qemu doesn't support the 'transaction' command, libvirt can't make qemu do what VDSM wants. Basically, the 'blockdev-snapshot-sync' command in qemu 1.0 lacks the ability to reuse qcow2 metadata already present in the file pre-created by VDSM; this wasn't added until the 'transaction' command of qemu 1.1.