How are new LUNs discovered by ESX Server?

A.
A reboot operation is required to detect newly presented LUNs.

B.
ESX Server automatically detects new LUNs as they are presented.

C.
ESX Server periodically performs a rescan operation to detect any new LUNs.

D.
A rescan operation is required every time a new LUN is added.

Explanation:
iSCSI SAN Configuration Guide, page 26.
The VMkernel discovers LUNs when it boots, and those LUNs are then visible in the vSphere Client. If changes are made to the LUNs, you must rescan to see those changes.
* New LUNs created on the iSCSI storage
* Changes to LUN access control
* Changes in connectivity