Data General AViiON 4600 Series, Customer Documentation

Page: 72 / 266

Setting Up and Installing a SCSI Bus
4-4
014–002091
A second SCSI bus uses the same recommended device ID assignments as the first.
System software recognizes adevice on either bus by acombination of the device ID
and the controller number (indicted in the () portion of the DG/UX pathname). For
example, sd(ncsc(1)0) identifies the first hard disk supported by the second SCSI (B)
controller. Refer to your DG/UX documentation or Chapter 5 for more information
about device specifications.
NOTE: ID assignments do not need to reflect the physical positioning of devices
along the SCSI bus; a drive at the physical end of the bus can have a higher
or lower device identification number than another drive closer to the SCSI
controller in the computer unit.
The DG/UX operating system allows the configuration of any SCSI device at
any unique and valid SCSI device ID number. However, other software such
as device drivers could limit the use of certain device ID numbers to specific
types of devices. Check the drive manual(s), and the documentation for any
customized software you plan to run on your system, for further SCSI ID
restrictions.
The automatic boot sequence for your computer system looks for a disk at
device ID 0 on the first SCSI controller. Therefore, you should assign SCSI
device ID 0, Controller 0, to the system (root) disk. Unless you manually
change the automatic boot path, this disk will boot automatically when you
power up the computer system. You also use the SCSI ID of a device when
booting it directly (using the SCM
command) or to change the
automatic boot path, as described in Chapter 5.
Figure 4Ć2 shows an example of a valid SCSI ID configuration that follows the pattern
of recommended ID assignments.