11:36 a.m.
After looking into a qemu a bit, I believe the snapshot operation on
the disk in oVirt is not a live snapshot, because the guest VM will be
paused by qemu when the snapshot is undergoing. That is what qemu
monitor command "snapshot_blkdev" does and VDSM depends on that command
in low level. Most likely, the pausing time is non-trival for a
normal snapshot.
On 2012-6-29 0:37, Itamar Heim wrote:
On 06/28/2012 09:20 AM, Eric Blake wrote:
> 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.
>
ok, i guess the question is then when qemu 1.1 is expected in fedora
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Shu Ming <shuming(a)linux.vnet.ibm.com>
IBM China Systems and Technology Laboratory