[libvirt] A couple of questions on snapshot-create/ snapshot-create-as
Hi (Eric?), I got a couple of questions for 'snapshot-create' / 'snapshot-create-as' : 1/ can '--disk-only' option (when used with virsh snapshot-create-as) be run on an offline guest and generate an 'external snapshot' ? Or a running guest is needed? 2/ Can anyone point me to a bit more verbose info on these below options while creating snapshots? --quiesce quiesce guest's file systems --atomic require atomic operation --reuse-external reuse any existing external files Thanks. /kashyap
On 04/30/2012 06:17 AM, Kashyap Chamarthy wrote:
Hi (Eric?),
I got a couple of questions for 'snapshot-create' / 'snapshot-create-as' :
1/ can '--disk-only' option (when used with virsh snapshot-create-as) be run on an offline guest and generate an 'external snapshot' ?
Not yet, but it's on my list of things to add.
Or a running guest is needed?
For now, this is true.
2/ Can anyone point me to a bit more verbose info on these below options while creating snapshots?
--quiesce quiesce guest's file systems --atomic require atomic operation --reuse-external reuse any existing external files
http://libvirt.org/html/libvirt-libvirt.html#virDomainSnapshotCreateXML (Yuck - our online doc conversion loses paragraph breaks, and isn't understanding how to mark up parameter names). --quiesce maps to VIR_DOMAIN_SNAPSHOT_CREATE_QUIESCE, which requests that if the guest has a guest agent running, then connect to that agent and request that the file systems be frozen before taking the snapshot (that way, you can then directly boot the snapshot without having to run fsck). --atomic maps to VIR_DOMAIN_SNAPSHOT_CREATE_ATOMIC. If you are using qemu 1.0 or earlier, this flag will fail unless you only snapshot a single disk; if you are using qemu 1.1 or later, this flag will ensure that the qemu monitor command 'transaction' is used to ensure an atomic snapshot. Omitting the flag has no change of behavior on qemu 1.1, but on qemu 1.0 or earlier, the snapshot is attempted, but if you fail partway through, then you may be left with a domain where half the disks had a snapshot and the other half did not. --reuse-external maps to VIR_DOMAIN_SNAPSHOT_CREATE_REUSE_EXT, which states that rather than having libvirt create the snapshot file from scratch, you will pre-create the file. This is useful for applications like VDSM that want the snapshot to be pre-created with a relative backing file name in the qcow2 metadata (libvirt would create it with an absolute backing file name). -- Eric Blake eblake@redhat.com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
On 04/30/2012 06:48 PM, Eric Blake wrote:
On 04/30/2012 06:17 AM, Kashyap Chamarthy wrote:
Hi (Eric?),
I got a couple of questions for 'snapshot-create' / 'snapshot-create-as' :
1/ can '--disk-only' option (when used with virsh snapshot-create-as) be run on an offline guest and generate an 'external snapshot' ?
Not yet, but it's on my list of things to add.
Or a running guest is needed?
For now, this is true.
2/ Can anyone point me to a bit more verbose info on these below options while creating snapshots?
--quiesce quiesce guest's file systems --atomic require atomic operation --reuse-external reuse any existing external files
http://libvirt.org/html/libvirt-libvirt.html#virDomainSnapshotCreateXML
(Yuck - our online doc conversion loses paragraph breaks, and isn't understanding how to mark up parameter names).
--quiesce maps to VIR_DOMAIN_SNAPSHOT_CREATE_QUIESCE, which requests that if the guest has a guest agent running, then connect to that agent and request that the file systems be frozen before taking the snapshot (that way, you can then directly boot the snapshot without having to run fsck).
I'm assuming you're talking about this 'agent' -- http://wiki.qemu.org/Features/QAPI/GuestAgent
--atomic maps to VIR_DOMAIN_SNAPSHOT_CREATE_ATOMIC. If you are using qemu 1.0 or earlier, this flag will fail unless you only snapshot a single disk; if you are using qemu 1.1 or later, this flag will ensure that the qemu monitor command 'transaction' is used to ensure an atomic snapshot. Omitting the flag has no change of behavior on qemu 1.1, but on qemu 1.0 or earlier, the snapshot is attempted, but if you fail partway through, then you may be left with a domain where half the disks had a snapshot and the other half did not.
--reuse-external maps to VIR_DOMAIN_SNAPSHOT_CREATE_REUSE_EXT, which states that rather than having libvirt create the snapshot file from scratch, you will pre-create the file. This is useful for applications like VDSM that want the snapshot to be pre-created with a relative backing file name in the qcow2 metadata (libvirt would create it with an absolute backing file name).
Thanks Eric, for the clarification and detailed info. -- /kashyap
participants (2)
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Eric Blake -
Kashyap Chamarthy