VMS Help BACKUP Command, Qualifiers, /REWIND  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /REWIND
       /NOREWIND (default)

    Input or Output Save-Set Qualifier

    As an input save-set qualifier, causes the input tape reel to be
    rewound (/REWIND) or not rewound (/NOREWIND) to beginning-of-tape
    (BOT) before BACKUP searches for the save-set name specified in
    the input specifier.

    As an output save-set qualifier, specifies that the output
    magnetic tape is to be rewound and initialized before the
    save operation begins (/REWIND) or that the tape is neither
    to be rewound nor initialized before the save operation begins
    (/NOREWIND). Initializing the tape removes access to any existing
    data on the tape. If you want to start processing at BOT, and the
    magnetic tape is already positioned beyond BOT, specify /REWIND.
    Otherwise, the magnetic tape begins (or resumes) processing from
    the logical end-of-tape (EOT) marker.

    Use the /[NO]REWIND qualifier for magnetic tape save sets only.