Digital Equipment PRIORIS ZX 5000 MP, User Manual

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Expanding Your Server
3-40
Active negation outputs reduce the chance of data errors by actively driv-
ing both polarities of the SCSI bus and avoiding indeterminate voltage
levels and common-mode noise on long cable runs. The SCSI output driv-
ers can directly drive a 48 mA, single-ended SCSI bus with no additional
drivers.
No additional logic, termination, or resistor loads are required to connect
up to seven 8-bit narrow SCSI devices or up to fifteen 16-bit wide SCSI
devices to each SCSI-2 channel on the main logic board.
SCSI Configuration Guidelines
Your server configuration, SCSI adapter(s), and all SCSI devices must
work together for optimum performance. When installing SCSI devices,
use the following guidelines:
•
The last physical SCSI devices on each end of the SCSI bus must
be terminated. Your server is supplied with the necessary cables
and terminators. If your SCSI device came with terminators in-
stalled, you must remove or disable the terminator from the device
before you complete the installation.
Refer to your SCSI device’s manufacturer documentation for the terminator lo-
cation.
•
Each SCSI device (including the SCSI controller) must be config-
ured with a unique ID number. SCSI controllers usually default to
ID 7. The SCSI CD-ROM drive defaults to ID 5. Use the remaining
IDs 0 through 4 and 6 (narrow and wide adapters) and 8 through
15 (wide adapters only) to configure hard disk drives and other
SCSI devices. Hard disk drives should be configured to start with
SCSI ID 0 and the lower ID numbers. Also, note that the storage
backplane has pre-configured ID settings.
Refer to “SCSI Drive IDs” later in this chapter.