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

       /DISK[=device-name[:]]

    Specifies the disk whose quotas are to be examined. By default,
    the current default disk (defined by the logical name SYS$DISK)
    is examined.