How Vms Uses The Dssi Device Parameters - DEC 4000 Model 200 Operation Manual

The SYSTEMID parameter provides a number that uniquely identifies the
device to the operating system. This parameter may need to be modified
only when replacing a device. Only Customer Services representatives and
qualified self-maintenance customers can remove devices.
B.2 How VMS Uses the DSSI Device Parameters
This section describes how the operating system uses the parameters to
form 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
where:
NODENAME is a unique node name and u is the unit number.
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
where:
ALLCLASS is the allocation class for the system and devices, and u is a
unique unit number.
Using the KFQSA storage adapter and mass storage expanders, you can
fill multiple DSSI busses: the KA660 CPU provides one bus, and a second
and third DSSI bus can be added using the KFQSA. 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 busses,
as the unit numbers for all DSSI devices connected to a system's associated
DSSI busses must be unique.
Figure B–1 illustrates the need to program unit numbers for a system using
more than one DSSI bus and a nonzero allocation class. In the case of
the nonzero allocation class, the operating system sees two of the ISEs as
having duplicate device names, which is an error, as all unit numbers must
be unique.
Programming Parameters for DSSI Devices B–3