WBM_MSG_LOWER is one of three system parameters that are
    available for managing the update traffic between a master
    write bitmap and its corresponding local write bitmaps in an
    OpenVMS Cluster system. The others are WBM_MSG_INT and WBM_MSG_
    UPPER. These parameters set the interval at which the frequency
    of sending messages is tested and also set an upper and lower
    threshold that determine whether the messages are grouped into
    one SCS message or are sent one by one.

    WBM_MSG_LOWER is the lower threshold for the number of messages
    sent during the test interval that initiates single-message mode.
    In single-message mode, the writes issued by each remote node
    are, by default, sent one by one in individual SCS messages to
    the node with the master write bitmap. If the writes sent by
    a remote node reach an upper threshhold of messages during a
    specified interval, single-message mode switches to buffered-
    message mode.

    The minimum value of WBM_MSG_LOWER is 0 messages per interval.
    The maximum value is -1, which corresponds to the maximum
    positive value that a longword can represent. The default is
    10.

    WBM_MSG_LOWER is a DYNAMIC parameter.