The number assigned to the address space that a host uses to access a logical drive.
Each host has its own Logical Unit Number (LUN) address space and will, therefore, allow the same LUN to be used by different host groups
When access to a logical drive is granted to a host group, all of the hosts within the host group will share the same LUN to access the logical drive.
Important: The same LUN may not be used twice by a host group or host to access a logical drive. A unique LUN must be used.