1) Virtual disk 
In storage virtualization, virtual disk (VD) or vdisk is a virtual logical disk or volume with which a computer or application performs I/O operations. Generally it is provided by a storage-virtualization device that is a part of storage area network (SAN).{cn|date=February 2013} {As of | 2012} the term vdisk is used in HP EVA disk arrays{citation...
Virtual Disk