Host A and B can both access LUNs one to ten in a single SAN, but Host B cannot access LUN 11. What is the likely cause of this issue?

The situation indicates that both hosts can access LUNs one to ten, suggesting that the connection to the SAN and access to those specific LUNs is functioning correctly. However, the fact that Host B cannot access LUN 11 points towards a permissions or configuration issue rather than a hardware failure.

The most probable cause of Host B being unable to access LUN 11 is the incorrect HBA World Wide Port Name (WWPN). Each host has a unique WWPN that is used by the SAN to identify and manage access rights. If Host B has an incorrect WWPN configured, it will lack the necessary permissions to access specific LUNs while still being able to access those it is permitted for, such as LUNs one to ten.

While other options like a faulty fiber HBA, an incorrect HBA software version, or a defective HBA could affect access to the SAN overall, they would not typically lead to a selective denial of access just for one particular LUN. Confirming that the WWPN is correctly set is crucial for ensuring access to all required LUNs in the SAN environment.