Technical data

C.1 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 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