In computer storage, a logical unit number, or LUN, is a number used to identify a logical unit, which is a device addressed by the SCSI protocol or by Storage Area Network protocols that encapsulate SCSI, such as Fibre Channel or iSCSI.
[1] A LUN may be used with any device which supports read/write operations, such as a tape drive, but is most often used to refer to a logical disk as created on a SAN.
How to select a LUN: In the early versions of SCSI, an initiator delivers a Command Descriptor Block (CDB) to a target (physical unit) and within the CDB is a 3-bit LUN field to identify the logical unit within the target.
Others have a small number of logical units that correspond to separate physical devices and have fixed LUNs.
The full device's address is made from the: In the Unix family of operating systems, these IDs are often combined into a single "name".
Presently Solaris, HP-UX, NCR, and others continue to use "c_t_d_s_" nomenclature, while AIX has abandoned it in favor of more familiar names.