98 Sun Fire 280R Server Owner’s Guide • January 2001
About the Small Computer SystemInterface (SCSI) Port
External Small Computer System Interface (SCSI) devices aresupported via a 68-pin
SCSI connector located on the system’s back panel. This bus is UltraSCSI-capable (40
Mbytes per second) and can support additional external, single-ended, wide or
narrow SCSI devices. The external SCSI bus is separate from the internal SCSI bus
for removable media devices and internal disk drives. See “Reference for the
UltraSCSI Connector” on page 208 for a diagram and pinout of the external SCSI
connector.
The external SCSI bus will support up to four external SCSI tape devices if the bus is
used exclusively for tape devices. When other types of SCSI devices are present on
the bus, a maximum of two SCSI tape devices are supported on the external SCSI
bus.Additional external tape devices can be supported by installing appropriate PCI
host adapter cards.

Target Devices

Up to 12 Sun-compensated devices can operate on the external SCSI bus at 20
Mbytes per second. For UltraSCSI performance of 40 Mbytes per second, no more
than seven devices may be connected. Targetaddresses for the external SCSI bus
(also known as SCSI IDs) are available in a range of 0through 15. Target address 7 is
reserved for the SCSI host adapter located on the main logic board. All devices on
the bus must have unique target addresses.
The addresses for the internal Digital VideoDisc-Read Only Memory (DVD)
drive (6) and tape drive (4 or 5) are determined by jumpers located on the drives. If
the DVD and tape drives have been factory-installed, they are configured with the
correct addresses for the system. Internal disk drives use 0 and 1.

Configuration Bus Lengths

For UltraSCSI performance on the external SCSI bus, you must adhere to the
following bus length restrictions for daisy-chained SCSI devices:
■For one to three devices, the maximum bus length is 9.84 feet (3 meters)
■For four to seven devices, the maximum bus length is 4.92 feet (1.5 meters)
Youmust include the Sun Fire 280R server internal bus length of .2226 feet
(.067 meter) in your bus length calculations.