About The Scsi Removable Media Bays And The External Scsi Port - Sun Microsystems Enterprise 250 Owner's Manual

About the SCSI Removable Media Bays
and the External SCSI Port
The removable media assembly located at the top front of the system provides
mounting bays for two 5.25-inch, half-height (1.6-inch) SCSI devices. The upper SCSI
bay (directly below the diskette drive bay) houses a CD-ROM drive. The lower bay
accommodates a second SCSI device, such as an 8-mm tape, a 4-mm DDS-2 or DDS-3
tape, or a quarter-inch cassette tape drive. Both SCSI removable media bays are
connected to the same SCSI bus as the internal disk drives. While this bus supports
wide SCSI operation for the internal disk drives, the removable media portion of the
bus operates in narrow SCSI mode only. The removable media assembly can
accommodate wide SCSI (68-pin) devices, however these devices require a
50-to-68-pin adapter cable, and operate in narrow SCSI mode only.
External SCSI devices are supported via a 68-pin SCSI connector located on the
system's rear 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 SCSI Connector" on page 267
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 15 devices can operate on the external SCSI bus at 20 Mbytes/sec. For
UltraSCSI performance of 40 Mbytes/sec, 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 and tape drives 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.
Chapter 4 Hardware Configuration 67