Hello Kevin, Am Freitag 12 August 2011 10:04:07 schrieb Kevin Wolf: > Am 12.08.2011 09:18, schrieb Philipp Hahn: > > On Thursday 11 August 2011 12:00:46 Kevin Wolf wrote: > >> Am 11.08.2011 00:08, schrieb Eric Blake: > >>> Libvirt currently has a bug in that it only saves <domain>/<uuid> > >>> rather than the full domain xml along with a checkpoint - if any > >>> devices are hot-plugged (or in the case of offline snapshots, if the > >>> domain configuration is changed) after a snapshot but before the > >>> revert, then things will most likely blow up due to the differences in > >>> devices in use by qemu vs. the devices expected by the snapshot. > >> > >> Offline snapshot means that it's only a disk snapshot, so I don't think > >> there is any problem with changing the hardware configuration before > >> restoring it. > >> > >> Or does libvirt try to provide something like offline checkpoints, where > >> restoring would not only restore the disk but also roll back the libvirt > >> configuration? > > > > Try to load a VM state with the memory size changed in between and your > > VM is busted; been there, experienced that :-( So it's nice to do a > > snapshot before you play with your virtual hardware configuration and can > > go back there if things go wrong. > > > > For -loadvm to work you have to call kvm with the nearly same command > > line arguments again; what may change you probably know better than me. > > For I thinks it's essential to store the VM consiguration with the > > snapshot, which would be the qemu command line arguments, which is > > equivalent to libvirts XML description. > > Yes, I understand this. I was talking about snapshots taken while the VM > is shut off, where it's not as clear. I think is very useful for offline snapshots too, since your VM might depends on the exact qemu command line: think of (incomplete) RAIDs or udevs persistent MAC address rules. > But for consistency it's probably > better to do the same with offline and online snapshots, so what libvirt > implements (or was it only Eric's plan?) is fine here. Currently as of libvirt-0.9.4 the domain configuration is not saved with the snapshot. I have implemented that for our internal 0.8.4 version as a working proof-on-concept, but Eric is now reviewing the whole picture. Sincerely Philipp -- Philipp Hahn Open Source Software Engineer hahn univention de Univention GmbH Linux for Your Business fon: +49 421 22 232- 0 Mary-Somerville-Str.1 D-28359 Bremen fax: +49 421 22 232-99 http://www.univention.de/
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