How Openvms Axp Uses The Dssi Device Parameters - DEC 4000 600 series Owner's Manual

Setting and Examining Parameters for DSSI Devices
This section describes how the OpenVMS AXP operating system
How OpenVMS
AXP Uses the uses the parameters to form unique identifiers for each device.
Configurations that require you to assign new unit numbers for
DSSI Device
devices are also described.
Parameters
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With DEC 4000 AXP systems, you can fill multiple DSSI buses:
buses A–D (slot numbers 0–3). Each bus can have up to seven
DSSI devices (drive IDs 0–6). When more than one bus is being
used, and your system is using a nonzero allocation class, you
need to assign new unit numbers for devices on all but one of the
DSSI buses, since the unit numbers for all DSSI storage devices
connected to a system's associated DSSI buses must be unique.
Figure 6–7 illustrates the problem of duplicate operating system
device names for a system that is using more than one DSSI
bus and a nonzero allocation class. In the case of the nonzero
allocation class, the operating system sees four of the devices
as having duplicate device names. This is an error, as all unit
numbers must be unique. The unit numbers for one of the two
DSSI buses in this example need to be reprogrammed.
6–28 System Configuration
With an allocation class of zero, the operating system can
use the default parameter values to provide each device with
a unique device name. The operating system uses the node
name along with the device logical name in the following
manner:
NODENAME$DIAu
NODENAME is a unique node name and u is the unit
number.
With a nonzero allocation class, the operating system uses
unit number values to create a unique device name. The
operating system uses the allocation class along with the
device logical name in the following manner:
$ALLCLASS$DIAu
ALLCLASS is the allocation class for the system and devices,
and u is a unique unit number.