What Is the Logical Unit Number (LUN) and How Does It Work?

What exactly is a LUN? It stands for logical unit number in short. It is a number used to identify the logical unit in computer storage. The logical unit is a device accessed by SCSI or Storage Area Network protocols that contain iSCSI (such as Fibre Channel or iSCSI).

LUNs can refer to logical disks established on a SAN, although they are most usually used to refer to devices that allow read/write operations, such as tape drives. The word "LUN" is also widely used to refer to the logical disk itself, which is technically erroneous.

How Does LUN Work?

LUN configuration varies by system. The host will assign a logical unit number when it scans the SCSI device and finds one. The LUN defines a specific logical unit for the SCSI initiator when paired with information such as the target port identifier.

The logical unit can be a component of a storage drive and the complete storage drive in one or more storage systems, or it can be all parts of numerous storage drives, such as a hard disk drive and a solid-state drive.

The LUN might be a single drive or partition, or several storage devices or partitions. In any case, the logical unit is treated as a single device, and its number is used to identify it. LUN capacity restrictions differ per system.

In a storage area network, the LUN is at the heart of block storage array administration. Because logical IDs may be used to provide access and control rights, LUNs can make storage resource management easier.

Types of LUNs

Performance and reliability are influenced by the underlying storage structure and logical unit kinds. The following are some examples of LUNs:

• Mirrored LUN. For data redundancy and backup, a mirrored LUN is a fault-tolerant LUN having identical copies on two physical disks.

• Concatenated LUN. A concatenated LUN is a logical unit or volume that incorporates several LUNs.

• Striped LUN distributes I/O requests over many physical disks, potentially improving performance.

• Striped LUN. Data and parity information are dispersed among three or more physical disks in a striped LUN with parity. You may rebuild the data from the information on the remaining disks if the actual drive dies. Write performance may be affected by parity computations.

LUN Uses

The most common application for LUNs is as a storage device identification. However, each LUN type may be used differently. A basic LUN, for example, is used to designate a portion or the full physical disk. A spanned LUN is an identifier for a LUN that spans two or more physical drives.

The mirrored LUN is used to tell the data on one disk to be copied to the second disk in the event that one disk dies.

In SANs, LUNs can be utilized for zoning and masking or virtualized to map multiple physical LUNs.

Why do we need LUNs?

As previously stated, in a SCSI context, a LUN is an address that allows one system to locate a data storage, often a disk partition, in a broader network. Multiple LUNs can exist on a same physical drive, each corresponding to a separate disk partition. We can control which systems in our SAN are exposed to each other by targeting and masking certain LUNs. We can customize our SAN environment to meet the demands of our facility with this level of control.