You can override the default IDs by jumpers on each disk board. Each disk has an ID_ENABLE jumper and four ID jumpers. If the ID_ENABLE jumper is not installed, the disk drive uses the default SCSI ID. If the ID_ENABLE jumper is installed, the disk drive uses the ID specified by the four ID jumpers located on the disk board (an installed jumper indicates a logical 1).
For Enterprise 4500 and 5500 servers, default disk drive ID numbers are chosen so that IDs 4, 5, 6, and 7 are unlikely to be assigned to disk drives. These IDs are in slots 0 and 1, which are normally taken by a CPU/Memory+ board (slot 0) and an I/O board (slot 1).