So for all lease-holding vms, push the lease to a different storage domain (on different storage hardware), apply the upgrade and then push the leases back? And that can be done whilst the VMs are running? Leases must be frequently renewed, so I guess no particular reason why not.
If you have the storage leases on another hardware then you do not have the same problem I have; unless you are talking about upgrading the hardware of the storage domain that holds the leases. General: you can change the lease on a running VM. But (speaking for 4.2) you have to set it to no lease first.
Does that work for the SPM and hosted engine as well?
I think the hosted engine has it's own kind of storage lease, but I can't say anything to that. SPM does not have a storage lease it should be hardware (ie it's one of the hypervisors) not a VM.
I'm guessing this doesn't help with an unmanaged contoller failover. Anecdotally, that seems to happen a bit faster for me than a managed one, which is also odd.
Yeah, all my ideas are just for planned maintenance.