System information

Programming Parameters for DSSI Devices
E-2
VAX 4000 Model 108 User Information
__________________________ Note ____________________________
On some systems, an optional DSSI daughter card (KFDDA--BB) provides a second DSSI
interface, so there are two DSSI buses with the same specifications.
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DSSI Device Parameters
Seven principal parameters are associated with each DSSI device:
• Bus Node ID
• ALLCLASS
• UNITNUM
• FORCEUNI
• NODENAME
• SYSTEMID
• 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 the 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.