/sys$common/syshlp/helplib.hlb Sys Parameters, ACP_MULTIPLE  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    ACP_MULTIPLE enables (1)  or disables (0) the default creation of
    a separate disk XQP cache for each volume mounted on a different
    device type. Prior to Version 4.0, a separate ACP process was
    created for each device type if this parameter was enabled.
    Because ACP operations are now handled by the per process XQP,
    such separate processes are no longer created. In general, having
    multiple caches is unnecessary. One large cache is more efficient
    than several small ones. ACP_MULTIPLE can be overridden on an
    individual-volume basis with the DCL command MOUNT.

    ACP_MULTIPLE is an AUTOGEN and DYNAMIC parameter.