For disks connected using Fibre Channel-Arbitrated Loop (FC-AL or FC), the disk ID is an integer from 16 to 126.
The disk ID corresponds to the disk shelf number and the bay in which the disk is installed. The lowest disk ID is always in the far right bay of the first disk shelf. The next higher disk ID is in the next bay to the left, and so on. You can view the device map for your disk shelves with the fcadmin device_map command.
For more information about the addressing map for your disk shelf, see the hardware guide for the disk shelf.