VMS Help SET, FILE, /AI_JOURNAL, Description  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    The SET FILE/AI_JOURNAL command marks one or more RMS files
    for after-image journaling. You can also specify certain
    characteristics of the journal with this command, including its
    file specification, whether it is to be created, its initial
    size, and its default extension quantity. The SET FILE/NOAI_
    JOURNAL command unmarks a file for after-image journaling. After
    a data file is marked for after-image journaling with the SET
    FILE/AI_JOURNAL command, the following events occur whenever the
    file is opened by RMS for write operations:

    o  The journal is opened.

    o  All subsequent modifications to the data file are recorded in
       the journal.

                                   NOTE

       To be able to recover the data file at a later time,
       you must make a backup copy of the data file, even if it
       contains no data.

    You must use the FILE keyword to specify a journal. By default,
    any portions of the file specification that you omit will be the
    same as the data file that is to be journaled, but with the file
    type RMS$JOURNAL. That is, if you issue the following command,
    then, by default, the file specification for the after-image
    journal is JOURNAL_DISK:PAYROLL.RMS$JOURNAL:

    $ SET FILE/AI_JOURNAL=(FILE=JOURNAL_DISK:) FINANCE_DISK:PAYROLL.DAT

    You should always keep the journal for after-image applications
    on a different volume from that of your data file. If recovery
    becomes necessary, you will be able to perform after-image
    recovery only if a backup copy of the data file is available.
    Use the FILE keyword to specify the journal location.

    Use the SET FILE/NOAI_JOURNAL command to unmark a file for after-
    image journaling. After you use the SET FILE/NOAI_JOURNAL command
    for a file, modifications to that data file will no longer be
    written to the journal.

    You must use the SET FILE/NOAI_JOURNAL command before you can
    delete a file that has been marked for after-image journaling.