How to prevent virtual machines running twice on the disk images?

[Theo Band <theo.band@xxxxxxxxxxxxx>]

I use KVM on two identical centos5 hosts.

I can live migrate the virtual machines from one to the other and it
works great. Once I do this, I can see VM definitions on both hosts
using virt-manager or virsh list --all
On one machine the VM is running, on the other it reports "shut off".
The disk images are accessible to both host machines and I want to have
only one running a the time (of course). If the VM locks up, I could by
mistake think that the machine is not running and try to start it on the
wrong host.

My question is, how can I prevent host A from starting a "shut off" VM
that actually has been migrated to host B? The VM could actually be
running on any another host. It could also have been crashed. The most
simple solution would be some sort of lock file placed next to the disk
image location, so seen by all hosts. But perhaps there is another way
of working with virt-manager that I am not aware of?

Theo
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