Multi-Initiator Support - Sun Microsystems Enterprise 250 Owner's Manual

Multi-initiator Support

The SCSI implementation of the system includes multi-initiator support: any external
host adapter on the bus can drive Termpower. This means that if the system should
lose power, the devices on the SCSI bus (except those powered by the system) can
continue to operate.
Configuration Rules
For Fast/Wide performance, you can connect up to 15 devices to the external SCSI
bus. For UltraSCSI performance, no more than seven devices may be connected. Each
device must have a unique target address (SCSI ID) in the range from 0 to 15.
You cannot assign target address 7 to any device; it is reserved for the host adapter
on the main logic board.
For UltraSCSI performance on the external SCSI bus, all cables used must be
UltraSCSI-compliant, and you must adhere to the following bus length restrictions:
4 For 1 to 3 devices, the maximum bus length is 3 meters (9.84 feet)
4 For 4 to 7 devices, the maximum bus length is 1.5 meters (4.92 feet)
You must include the Enterprise 250 internal bus length (0.5 meter/1.7 feet) in your
bus length calculations.
For Fast/Wide performance on the external SCSI bus, the maximum SCSI bus length
for daisy-chained SCSI devices is 6 meters (19.7 feet), including the Enterprise 250
internal bus length (0.5 meter/1.7 feet).
UltraSCSI devices can be mixed with non-UltraSCSI devices on the same bus. The
UltraSCSI devices will still operate at UltraSCSI speeds (40 Mbytes/sec), provided
that the rules for UltraSCSI cabling, bus length, termination, and target devices are
followed.
If all external SCSI devices use 68-pin connectors, connect all non-Sun devices to the
system first and connect a Sun autoterminating device to the end the chain.
If external mass storage devices consist of 68-pin devices and 50-pin devices, connect
the Sun 68-pin devices to the system first and terminate the chain with a 50-pin
device and its terminator. The 68-pin device connected to the 68-50 pin adapter cable
must be autoterminating in order to terminate the high-order bits.
If you install an internal tape drive in the system, you should assign it target
address 4 or 5. If you install an internal CD-ROM in the system, you should assign it
target address 6. If these drives have been factory-installed, they are configured with
the correct addresses for the system.
The removable media SCSI cable provides the termination for the internal SCSI bus.
Sun Enterprise 250 Server Owner's Guide ♦ Revision A, June 1998
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