RMS_SEQFILE_WBH can enable the RMS writebehind feature as a
    system default for any unshared sequential disk file if the
    file is opened for image I/O with write access specified.
    The possible settings are the following:

    Setting        Description

    0 (default)    Do not enable writebehind feature. Preserve prior
                   behavior of using writebehind only if the user
                   requests it by setting RAB$V_WBH in RAB$L_ROP.

    1              Enable writebehind feature as system default,
                   including the allocation of at least two local
                   buffers.

    RMS_SEQFILE_WBH is a DYNAMIC parameter.