About The External Scsi Port; Target Devices; Bus Length - Sun Microsystems Sun Enterprise 220R Owner's Manual

About the External SCSI Port

External SCSI devices are supported 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 161 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. Target addresses for the external SCSI bus
(also known as SCSI IDs) are available in a range of 0 through 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 CD-ROM (6) and tape drive (4 or 5) are determined by
jumpers located on the drives. If the CD-ROM and tape drives have been factory-
installed, they are configured with the correct addresses for the system. Internal disk
drives use 0 and 1.

Bus Length

For UltraSCSI performance on the external SCSI bus, you must adhere to the
following bus length restrictions for daisy-chained SCSI devices:
For 1 to 3 devices, the maximum bus length is 9.84 feet (3 meters)
For 4 to 7 devices, the maximum bus length is 4.92 feet (1.5 meters)
You must include the Sun Enterprise 220R server internal bus length of 2.952 feet
(0.9 meter) in your bus length calculations.
84 Sun Enterprise 220R Server Owner's Guide • October 1999