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

    Input or Output Save-Set Qualifier

    Defines the input or output specifier as a BACKUP save set.
    Normally, BACKUP treats specifiers that refer to disk files as
    Files-11 files and specifiers that refer to tapes as BACKUP save
    sets.

    You must specify the /SAVE_SET qualifier when the input or output
    specifier is a BACKUP save set on a Files-11 disk.