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

       /BACKUP
       /NOBACKUP

    Specifies that the Backup utility (BACKUP) records the contents
    of the file. The /NOBACKUP qualifier causes BACKUP to record the
    attributes of the file but not its contents. This qualifier is
    valid only for Files-11 Structure On-Disk Level 2 and 5 files.

    The /NOBACKUP qualifier is useful for saving files that contain
    unimportant data, such as SWAPFILES.