Space-efficient VDisks
A Virtual Disk (VDisk) can be configured as space-efficient, which means that it has both virtual and real capacity.
Virtual Capacity - VDisk storage that is available to hosts
Real Capacity - Physical storage from an MDisk that is allocated to a VDisk copy
For a fully allocated VDisk (all real capacity), virtual and real capacity are identical; however, in a space-efficient VDisk, virtual capacity can exceed real capacity.