LUN (Logical Unit Number):

• Physical drives or groups of RAID protected drives can be logically split into volumes known as logical volumes, commonly referred to as Logical Unit Numbers (LUNs). The use of LUNs improves disk utilization. For example, without the use of LUNs, a host requiring only 200 GB could be allocated an entire 1TB physical disk. Using LUNs, only the required 200 GB would be allocated to the host, allowing the remaining 800 GB to be allocated to other hosts.

• In the case of RAID protected drives, these logical units are slices of RAID sets and are spread across all the physical disks belonging to that set. The logical units can also be seen as a logical partition of a RAID set that is presented to a host as a physical disk.

• The capacity of a LUN can be expanded by aggregating other LUNs with it. The result of this aggregation is a larger capacity LUN, known as a meta-LUN.

LUN Masking:

• LUN masking is a process that provides data access control by defining which LUNs a host can access. LUN masking function is typically implemented at the front end controller. This ensures that volume access by servers is controlled appropriately, preventing unauthorized or accidental use in a distributed environment.

• For example, consider a storage array with two LUNs that store data of the sales and finance departments. Without LUN masking, both departments can easily see and modify each other’s data, posing a high risk to data integrity and security. With LUN masking, LUNs are accessible only to the designated hosts.