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Installing the A4800A Adapter
Setting SCSI IDs
Chapter 2 29
Setting SCSI IDs
You must assign a separate SCSI ID (0 through 15 for a 16-bit SCSI bus)
to the SCSI host bus adapter and each SCSI device. The priority of the
device on the SCSI bus is determined by the SCSI ID of the device. The
order of SCSI ID priorities (from highest to lowest) is 7, 6, 5, 4, 3, 2, 1, 0,
15, 14, 13, 12, 11, 10, 9, and 8. A device with SCSI ID 7 has the highest
priority, and one with SCSI ID 8 has the lowest.
When you are assigning SCSI IDs, we recommend you to give the SCSI
host bus adapter higher priority than the other SCSI devices on the bus.
SCSI ID 7 is the preset SCSI ID for the A4800A SCSI host bus adapter
(giving it the highest priority on the SCSI bus). Set each of the other
SCSI devices on the bus to one of the remaining SCSI IDs.
For a multi-initiator (High Availability [HA]) configuration, where
multiple SCSI host bus adapters are connected to the same SCSI bus, the
SCSI host bus adapter that carries most of the traffic must be assigned a
SCSI ID of 7 (giving it the highest priority). Later, you must change the
SCSI ID of each of the remaining SCSI host bus adapters on the bus from
the preset setting (7) to the next highest priority remaining SCSI IDs (for
example, 6, 5, 4, and so on).
If you plan to boot your system from a hard disk drive on the SCSI bus,
you must assign that drive the next highest priority unassigned SCSI ID.
If there is only one SCSI host bus adapter (SCSI ID = 7), the hard disk
drive would be assigned a SCSI ID of 6. If there are multiple SCSI host
bus adapters, the hard disk drive would be assigned the next highest
priority SCSI ID available after all of the SCSI host bus adapters have
been assigned higher priority SCSI IDs.
To change the SCSI ID of the A4800A host bus adapter, refer to
“Checking SCSI Bus Compatibility” on page 36.
The peripheral device SCSI IDs are usually set with jumpers or a switch
on the peripheral. Refer to the peripheral manufacturer’s instructions to
determine the ID of each device and how to change it.
IMPORTANT You must not have duplicate SCSI IDs on a SCSI bus; the system will
hang or crash if you have duplicate SCSI IDs on the bus.