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

    Displays all devices that currently have volumes mounted on them.

    If you specify a device name, only the characteristics of that
    device are displayed; however, if the device is not currently
    mounted, the command issues a message indicating there is no such
    device. If you specify a generic device name, the characteristics
    of all such devices that currently have volumes mounted are
    displayed.