[Libvir] Snapshots in Libvirt
Hi, Can anyone tell me on which version of libvirt, the snapshot functionality is planned to be implemented fos Xen and KVM? By snapshot I mean to be able to save the state of the machine in order to be able to revert to the snapshot. Best Regards, Gabriel Kaufmann Software Engineer Gabriel.Kaufmann@ericom.com<mailto:Gabriel.Kaufmann@ericom.com> Ericom Software Tel (Dir): +972 2 591 1700 Ext 754 Tel (Main): +972 2 591 1700 http://www.ericom.com Access Done Right Empower Enterprise-Wide Access to Microsoft(r) Terminal Server, Virtual Desktops and Legacy Applications
On Thu, Feb 28, 2008 at 06:33:13PM +0200, Gabriel Kaufmann wrote:
Hi,
Can anyone tell me on which version of libvirt, the snapshot functionality is planned to be implemented fos Xen and KVM?
By snapshot I mean to be able to save the state of the machine in order to be able to revert to the snapshot.
Can you provide pointers to descriptions of Xen and KVM support for this ? My take was that the main problem was with snapshotting support at the filesystem level, and I think only LVM has support for this, Daniel -- Red Hat Virtualization group http://redhat.com/virtualization/ Daniel Veillard | virtualization library http://libvirt.org/ veillard@redhat.com | libxml GNOME XML XSLT toolkit http://xmlsoft.org/ http://veillard.com/ | Rpmfind RPM search engine http://rpmfind.net/
On Thu, Feb 28, 2008 at 11:44:28AM -0500, Daniel Veillard wrote:
On Thu, Feb 28, 2008 at 06:33:13PM +0200, Gabriel Kaufmann wrote:
Hi,
Can anyone tell me on which version of libvirt, the snapshot functionality is planned to be implemented fos Xen and KVM?
By snapshot I mean to be able to save the state of the machine in order to be able to revert to the snapshot.
Can you provide pointers to descriptions of Xen and KVM support for this ? My take was that the main problem was with snapshotting support at the filesystem level, and I think only LVM has support for this,
It needs closely co-ordination between the HV & the filesystem and is not possible to implement in the general case. QEMU/KVM supports snapshots only if your disks are in QCow2 format. There's no way to co-ordinate its snapshots with LVM snapshotting. And if you're using raw partitions, iSCSI, FiberChannel, you're totally out of luck This is not to say we shouldn't impleemnt snapshots in the API for libvirt. Just that there will be *very* limited scenarios in which it will be usable Dan. -- |=- Red Hat, Engineering, Emerging Technologies, Boston. +1 978 392 2496 -=| |=- Perl modules: http://search.cpan.org/~danberr/ -=| |=- Projects: http://freshmeat.net/~danielpb/ -=| |=- GnuPG: 7D3B9505 F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 -=|
On Thu, Feb 28, 2008 at 04:48:19PM +0000, Daniel P. Berrange wrote:
On Thu, Feb 28, 2008 at 11:44:28AM -0500, Daniel Veillard wrote:
On Thu, Feb 28, 2008 at 06:33:13PM +0200, Gabriel Kaufmann wrote:
Hi,
Can anyone tell me on which version of libvirt, the snapshot functionality is planned to be implemented fos Xen and KVM?
By snapshot I mean to be able to save the state of the machine in order to be able to revert to the snapshot.
Can you provide pointers to descriptions of Xen and KVM support for this ? My take was that the main problem was with snapshotting support at the filesystem level, and I think only LVM has support for this,
It needs closely co-ordination between the HV & the filesystem and is not possible to implement in the general case. QEMU/KVM supports snapshots only if your disks are in QCow2 format. There's no way to co-ordinate its snapshots with LVM snapshotting.
okay,
And if you're using raw partitions, iSCSI, FiberChannel, you're totally out of luck
This is not to say we shouldn't impleemnt snapshots in the API for libvirt. Just that there will be *very* limited scenarios in which it will be usable
First question is really about support, i.e. how to activate it in QEMU/KVM, and the obvious second question is what happen if snapshoting can't or didn't work. The hypervisor in general doesn't care what kind of filesystems are being used by the domain, can't guess in the general case, hence how can it check whether this will work or not. Even if QEmu could detect the domain booted off a QCow2 disk, can it really detect that the domain used for example an iSCSI one and that trying to snapshot will just result in corruption, without being able to detect the problem and fail the operation. The main risk to me seems to come from suggesting an API which can fail silently and lead to data corruption, doesn't sound cool. Daniel -- Red Hat Virtualization group http://redhat.com/virtualization/ Daniel Veillard | virtualization library http://libvirt.org/ veillard@redhat.com | libxml GNOME XML XSLT toolkit http://xmlsoft.org/ http://veillard.com/ | Rpmfind RPM search engine http://rpmfind.net/
DV> Can you provide pointers to descriptions of Xen and KVM support DV> for this ? My take was that the main problem was with DV> snapshotting support at the filesystem level, and I think only LVM DV> has support for this, My understanding is that qcow2 supports coordinated memory+disk snapshots of QEMU machines. This is something that we definitely would like to be able to support in the CIM providers when it's available in libvirt. There is already a DMTF model around providing this sort of functionality. -- Dan Smith IBM Linux Technology Center Open Hypervisor Team email: danms@us.ibm.com
participants (4)
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Dan Smith -
Daniel P. Berrange -
Daniel Veillard -
Gabriel Kaufmann