SnapDrive supports the feature introduced in Windows Server 2008 R2 that enables you to add or remove a pass-through disk on a Hyper-V virtual machine without shutting down that virtual machine. This is sometimes called the hot add and remove feature.
A pass-through disk is a disk that is physically connected to a Hyper-V parent host and is assigned to a Hyper-V virtual machine as a SCSI hard disk for use by that virtual machine.
Adding a SCSI controller requires virtual machine downtime.