Planning a SCSI bus configuration
3-5
014–002250–01
Optional SCSI adapter board expansion controllers
An optional SCSI I/O expansion board contains two additional SCSI
controllers and connectors for external devices. You can configure
both controllers for either single–ended or differential operation.
None of the bus length for these controllers resides within the
AViiON 5500 or 550 series computer.
External devices
Most stand–alone SCSI drives or storage subsystems consume
internal cable, reducing the maximum length of your external
cabling. Refer to the manual that came with your subsystem(s) for
its internal SCSI bus length.
"
Use the following formula to calculate the length of your SCSI bus
cable.
Length of internal
SCSI cable for
each device
+
Length of each
connecting
cable
=
Total SCSI
bus length
Identifying SCSI drives
Each SCSI controller in your system has a unique identifying
number and ID, beginning with Controller 0 for the integrated bus.
(The controller ID parameter is used in configurations where a
SCSI bus is shared by more than one host, or dual–initiated. Refer
to your Operating manual for information about a dual–initiated
SCSI bus.)
Similarly, each drive on each SCSI bus has a unique identification
number (referred to as a SCSI ID or device ID). Since each SCSI
controller supports a bus with up to seven devices, SCSI ID values
range from 0 through 6.
System software recognizes a device by a combination of its
SCSI ID and the controller number for the bus that supports the
device; AViiON firmware and the DG/UX operating system use
these numbers within device naming syntax. For example,
sd(ncsc(1,7),0)
identifies the disk at SCSI ID 0 on the second SCSI
bus (SCSI controller number 1).
When you receive preinstalled devices, the drives’ SCSI ID numbers
are already set. Factory–set SCSI IDs are listed on a label attached
to your computer rear panel.
Assigning SCSI IDs
Before you connect a SCSI bus cable to your computer unit, make
certain each device on the bus has a unique SCSI ID; if you notice a
conflict, you will need to reassign device identifications by changing
jumpers on the drive(s).
Summary of Contents for AViiON 550 Series
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