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

       /VOLUME[=n]

    Requests that the output file be placed on a specified relative
    volume number of a multivolume set. If you specify /VOLUME
    without a number, the number defaults to the relative volume
    number of the input image file.

    If the /VOLUME qualifier is not specified, the file is placed in
    an arbitrary position within the multivolume set.