/sys$common/syshlp/helplib.hlb SET, DEVICE, Qualifiers, /DUAL_PORT  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /DUAL_PORT
       /NODUAL_PORT

    Controls whether the port seize logic in the device driver of
    the specified disk is to be enabled. This qualifier should be
    used only on disks that contain a dual port kit and have been
    dismounted.