How Openvms Axp Uses The Dssi Device Parameters - DEC 4000 AXP Service Manual

6.4.3.1 How OpenVMS AXP Uses the DSSI Device Parameters

This section describes how the OpenVMS AXP operating system uses the
parameters to create unique identifiers for each device. Configurations that
require you to assign new unit numbers for devices are also described.
• 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$DIAu
NODENAME is a unique node name and u is the unit number. For example,
R7BUCC$DIA0.
• With a nonzero allocation class, the operating system relies on 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. For example, $1$DIA0.
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 (bus nodes 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 6–14 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.
6–38 System Configuration and Setup