108 RS/6000 43P 7043 Models 150 and 260 Handbook
4.3.1.4 SCSI Device Addresses
The Ultra SCSI adapters support a maximum of 16 SCSI addresses,
including devices and adapters. The default address for an adapter is 7, but it
can easily be changed if necessary.
• All devices on the SCSI bus must have a unique SCSI ID.
• The SCSI bus address determines priority on the bus. Address priority
from highest to lowest is as follows:
• The addresses 7, 6, 5, 4, 3, 2, 1, 0 and 15, 14, 13, 12, 11, 10, 9, 8, with
addresses 15 through 8 being used in 16-bit configurations only.
• Generally, the highest priority is assigned to the adapter.
• For any single adapter in an 8-bit configuration, a maximum of seven
devices are permitted, provided that the supported configuration-specific
bus lengths are not exceeded.
• For any single adapter in a 16-bit configuration, a maximum of 15 devices
are permitted, provided that the supported configuration-specific bus
lengths are not exceeded.
• The default ID of the SCSI adapter in a single adapter configuration is 7.
All devices on that bus must have a unique ID from 0 to 6 (8 to 15 are also
valid if SCSI-wide); two different devices may not have the same SCSI ID.
In the high-availability configurations, the second adapter must have its
address changed to avoid conflicts.
• If a SCSI address is changed after the operating system is loaded, the
operating system must be stopped and loaded again to have the correct
configuration, or cfgmgr run.
• Stand-alone diagnostics always default to a SCSI ID of 7 when testing
SCSI adapters and devices. Choosing SCSI IDs other than 7 for both
adapters prevents problems when using stand-alone diagnostics on
systems in HA clusters or in multi-initiator configurations.
• Check the documentation for your specific SCSI subsystem to insure that
there are no SCSI ID conflicts if the adapters are addressed at ID(s) other
than 6 or 7.
The SCSI address switch for each device must be set while power to
the system unit is off. If the SCSI device is an external type, the external
device must be powered off only while switching the address. The
operating system determines the system configuration during IPL (or
during execution of cfgmgr).
Note