(Logical Unit Number) An identification scheme for storage disks that typically supports a small number of units addressed as LUN 0 through 7, 15 or 31 depending on the technology. For example, Fibre Channel supports 32 addresses (0-31). A LUN may refer to a single disk, a subset of a single disk or an array of disks. Derived from the SCSI bus technology, each SCSI ID address can be further subdivided into LUNs 0 through 15 for disk arrays and libraries. See SCSI.