Comment 3 for bug 2077009

But this will break any additional evacuation.
Assume that you have 10 hypervisor, one die, you evacuate let say 9 vms and they are evenly spread. Now another hypervisor die and you have a problem, because VM cannot be evacuated anymore. It will fail with message: Instance has a complex allocation and cannot be moved (or something like that).

Also another possibility is that you never replace failed hypervisor. Let say it is an old HW and it just completely fail. You don't need to replace it because you have enough capacity. In that case you will need to manually fix placement for everything that was evacuated.