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

       /ACCESSED[=n]

    Requires OPER (operator) privilege.

    Specifies the number of directories to be maintained in system
    space for ready access. You can specify a value n in the range
    of 0 to 255. If you specify the qualifier /ACCESSED and omit
    the number of directories, a default value of 3 is used. If you
    specify a value greater than the current value, the new value is
    effective immediately; otherwise, the new value is not effective
    until the next time the volume is mounted.