(Alpha and Integrity servers) 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.