logical unit number (SAN) (LUN)
In storage area networks( SAN), the Logical Unit Number (LUN) or Logical Unit Name (LUN) is the smallest addressable unit for subcomponents of systems and devices.
The Logical Unit Numbers were introduced because SCSI only has a limited number of identification numbers available to address the system components such as the disk arrays. Each SCSI device has at least one and up to eight LUNs.
The logical unit number is assigned by the host when it recognizes a connected SCSI device. The Logicl Unit Number is used to identify the Logical Units( LU) for the SCSI bus. Such a logical unit can be a storage array or part of a storage array, for example a hard disk( HD) or a solid-state drive( SSD). Even a single partition can represent a Logical Unit and be identified with a Logical Unit Number.