On Mon, May 02, 2011 at 05:31:00PM -0600, Eric Blake wrote:
Consider the case of a guest that has multiple virtual disks, some residing on shared storage (such as the OS proper) and some on local storage (scratch space, where the OS has faster response if the virtual disk does not have to go over the network, and possibly one where the guest can still work even if the disk is hot-unplugged). During migration, you'd want different handling of the two disks (the destination can already see the shared disk, but must either copy the contents or recreate a blank scratch volume for the local disk).
Or, consider the case where a guest has one disk as qcow2 (it is not modified frequently, and benefits from sharing a common backing file with other guests), while another disk is raw (for better read-write performance). Right now, 'virsh snapshot' fails, because it only works if all disks are qcow2; and in fact it may be the case that it is desirable to only take a snapshot of a subset of the domain's disks.
There's a problem here, but I don't much like the solution. It's going to be very clumsy to extend (say) "virsh migrate" or virt-manager to support this. How about just adding flags into the disk XML, eg: <disk> ... <flags> <migrate>false</migrate> <snapshot>false</snapshot> </flags> </disk> (Don't sweat the details; the important point is that these are a property of the disk which is permanently attached to that disk through the XML). Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming blog: http://rwmj.wordpress.com Fedora now supports 80 OCaml packages (the OPEN alternative to F#) http://cocan.org/getting_started_with_ocaml_on_red_hat_and_fedora