The unique Virtual Disk Drive adds flexibility to expand the capacity of NAS. By using the built-in iSCSI initiator, the NAS can connect to the other iSCSI targets on the network and turn them into virtual disks, which become multiple single volumes on teh NAS. Up to 8 virtual disks can be stacked. The NAS serves as the storage stack chaining master.
This video shows you how to use the virtual disk to expand your storage.