Syntax option:

    NUMBER OF CLUSTER NODES IS number-nodes

    Sets the upper limit on the maximum number of VMS cluster nodes
    from which users can access the shared database. Specify this
    clause only if the database named in the ALTER DATABASE statement
    refers to a multifile 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. activity. Specify NUMBER OF
    CLUSTER NODES is set to 1, or use the SINGLE INSTANCE clause to
    enable these optimizations.

    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.