Re: [libvirt] RFC: APIs for managing a subset of a domain's disks
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.
--
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