On Tue, Mar 30, 2010 at 06:39:02PM -0400, Chris Lalancette wrote: > On 03/30/2010 05:26 PM, Eric Blake wrote: > > On 03/30/2010 02:52 PM, Matthias Bolte wrote: > >> Yep, if a domain it not running you'll just get a disk snapshot > >> without a memory snapshot. > > > > Is taking a halted disk snapshot something we might want to allow with a > > flag, though? For that matter, is this API useful for taking a disk > > snapshot and disregarding a memory snapshot even of a running VM? > > > > The problem with disgregarding a memory snapshot of a running guest is that it > is very easy to get inconsistent snapshots; that is, the guest could > have data cached in memory that is not on disk when you snapshot, and then you > have completely inconsistent results on disk. > > ESX allows you to do a disk only snapshot of a running guest, but they cheat; > they also have a way to quiesce the guest (force writes), thus ensuring a > consistent snapshot. > > Virtualbox doesn't give you a choice in the matter; if the guest is off when > you take a snapshot, you get a disk snapshot, and if it's on when you take a > snapshot, you get a disk+memory snapshot. > > Qemu allows both usages, although it must have the consistency problems I > mentioned above for a disk-only snapshot on a running guest. > > For now, I think we can stick with the disk-only semantic for shutoff guests, > and the disk+memory semantic for running guests. If it turns out that there > is a need for a disk-only semantic for running guests, this should be easy > to add later via a flag to virDomainSnapshotCreateXML. yes, that sounds a reasonable approach to me. Daniel -- Daniel Veillard | libxml Gnome XML XSLT toolkit http://xmlsoft.org/ daniel@xxxxxxxxxxxx | Rpmfind RPM search engine http://rpmfind.net/ http://veillard.com/ | virtualization library http://libvirt.org/ -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list