Hot-Add Disk to Clustered Virtual Machine from Hyper-V Manager

Q: I'm unable to hot-add a disk to a clustered virtual machine; what can I do?

A: As soon as you make a virtual machine a cluster resource, you need to stop using Hyper-V Manager to manage it because most operations become blocked. To configure a clustered virtual machine, use Failover Cluster Manager (or a management tool such as System Center Virtual Machine Manager). When you access the properties of the virtual machine from Failover Cluster Manager, the normal actions are available; for example, hot-adding a disk to the SCSI controller of a Hyper-V virtual machine.