VMS Help CMS, CREATE, LIBRARY, Qualifiers, /REFERENCE_COPY=directory-specification  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Specifies a valid VMS directory to be used for reference copies
    of library elements. The directory cannot be a CMS library, nor
    should it be a subdirectory of a CMS library directory. If you use
    the CREATE LIBRARY command to create a search list of more than
    one library, you should specify a reference copy directory for
    each library in the search list. If you specify only one reference
    copy directory for more than one library, CMS creates one library
    for the entire search list, not one library for each library in
    the search list. Wildcards are not allowed.
    /NOREFERENCE_COPY is the default.
    Use MODIFY LIBRARY to change this attribute on an existing library.