What is a LUN and what is it used for?

• A. A LUN is a Logical Unit Number used to present block storage to a host via iSCSI or FC; it represents a writable storage unit.
• B. A LUN is a file-level share that is accessed over NFS.
• C. A LUN is a backup snapshot used for recovery.
• D. A LUN is a network protocol for data transfer.

Answer: (A)

In a SAN, storage is presented to a server as raw block devices. A LUN is a Logical Unit Number that identifies a specific block storage object on the storage array and is presented to the host over protocols like iSCSI or Fibre Channel. The host sees this LUN as a writable block device, which you can partition and format with a filesystem to store data. It’s not a file-level share (that would be accessed via NFS/SMB), not a backup snapshot, and it’s not a network protocol itself. So the LUN serves as a writable block storage unit that the host can use directly.