We're evaluting KVM for Linux virtualization on a few projects. All is going well so far. But one of our requirements is the ability to add disk space to a running guest without rebooting or taking it offline. Is this possible with KVM?

The only thing I've found so far (but have not tested yet) is the ability to hotplug disks into the machine. If I go this route, then I could always add the new disk to an LVM volume group on the guest and then extend the chosen logical volume. The biggest downside to this approach is that over time we might end up with guests having variable numbers of virtual disks. The "real" disk space would be provided to the host over a SAN, so we can always add more space to the host whenever.