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

       /INDEX=position

    Specifies the location of the index file for the volume's
    directory structure. Possible positions are as follows:

    BEGINNING  Beginning of the volume
    MIDDLE     Middle of the volume (default)
    END        End of the volume
    BLOCK:n    Beginning of the logical block specified by n