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

    (Alpha only) FAST_PATH_PORTS is a static parameter that
    deactivates Fast Path for specific drivers.

    FAST_PATH_PORTS is a 32-bit mask. If the value of a bit in the
    mask is 1, Fast Path is disabled for the driver corresponding to
    that bit. A value of -1 specifies that Fast Path is disabled for
    all drivers that the FAST_PATH_PORTS parameter controls.

    Bit position zero controls Fast Path for PKQDRIVER (for parallel
    SCSI), and bit position one controls Fast Path for FGEDRIVER
    (for Fibre Channel). Currently, the default setting for FAST_
    PATH_PORTS is 0, which means that Fast Path is enabled for both
    PKQDRIVER and FGEDRIVER.

    In addition, note the following:

    o  CI drivers are not controlled by FAST_PATH_PORTS. Fast Path
       for CI is enabled and disabled exclusively by the FAST_PATH
       system parameter.

    o  FAST_PATH_PORTS is relevant only if the FAST_PATH system
       parameter is enabled (equal to 1). Setting FAST_PATH to zero
       has the same effect as setting FAST_PATH_PORTS to -1.

    For additional information, see FAST_PATH and IO_PREFER_CPUS.