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

       /INITIALIZE
       /NOINITIALIZE

    Command Qualifier

    Initializes an output disk or tape volume, making its entire
    previous contents unavailable. (/REWIND performs the same
    function for output tapes.) This qualifier is valid only when
    used with the /IMAGE qualifier during restore or copy operations
    or when saving files to a sequential-disk save set. The default
    is /INITIALIZE for Files-11 volumes and /NOINITIALIZE for
    sequential-disk volumes.