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C.1 DSSI Device Parameters
Seven principal parameters are associated with each DSSI device:
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Bus Node ID
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ALLCLASS
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UNITNUM
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FORCEUNI
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NODENAME
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SYSTEMID
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DSSI NODE ID
Each of these seven parameters, with the exception of the Bus Node ID, are
programmed and examined using the console-based Diagnostic and Utility
Program (DUP) driver utility. The Bus Node ID is physically determined by
jumpers on disk drive.
A brief description of each parameter follows.
The Bus Node ID parameter is provided by the jumpers on the disks. Each
DSSI bus can support up to eight nodes, 0–7. Each DSSI adapter and each
device count as a node. Hence, in a single-system configuration, a DSSI bus
can support up to seven devices, bus nodes 0–6 (with node 7 reserved for the
adapter); in a two-system DSSI VAXcluster configuration, up to six devices,
0–5 (with nodes 6 and 7 reserved for the adapters); in a three-system DSSI
VAXcluster configuration, up to five devices, 0–4 (with nodes 5, 6, and 7
reserved for the adapters).
The ALLCLASS parameter determines the device allocation class. The
allocation class is a numeric value from 0 to 255 that is used by the VMS
operating system to derive a path-independent name for multiple access paths
to the same device. The ALLCLASS firmware parameter corresponds to the
VMS SYSGEN parameter ALLOCLASS.
DSSI devices are shipped from the factory with a default allocation class of
zero. Each device to be served to a cluster should have a nonzero allocation
class that matches the allocation class of the system. Refer to the VMS
VAXcluster manual for rules for specifying allocation class values.
The UNITNUM parameter determines the unit number of the device. By
default, the device unit number is supplied by the jumpers on the drives.
Systems with multiple DSSI busses, as described later in this section, require
that the default values be replaced with unique unit numbers. To set unit
numbers and override the default values, you use the console-based DUP
C–2 Programming Parameters for DSSI Devices