Syntax option:

    NUMBER OF CLUSTER NODES number-nodes

    Sets the upper limit on the maximum number of VMS cluster nodes
    from which users can access the shared database. The default
    is 16 nodes. The range is 1 to 96 nodes. The actual maximum
    limit is the current VMS cluster node limit set by your system
    administrator.

    The Oracle Rdb root file data structures (.rdb) are mapped to
    shared memory. Each such shared memory copy is known as an Rdb
    instance. When there is only one copy of shared memory containing
    root file information, several optimizations are enabled to
    reduce locking and root file I/O during database activity. To
    enable these optimizations, specify NUMBER OF CLUSTER NODES 1, or
    use the SINGLE INSTANCE clause.

    MULTIPLE INSTANCE means that the Oracle Rdb root file data
    structures are mapped on different system and are kept consistent
    through disk I/O. Such systems can not benefit from single
    instance optimizations. MULTIPLE INSTANCE is the default.