VMS Help Sys Parameters, XFMAXRATE  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    XFMAXRATE limits the data transfer rate that can be set for
    DR32 devices. On some hardware configurations (especially those
    without interleaved memory), a high DR32 transfer rate could
    cause a machine check (CPU timeout). The OpenVMS I/O User's
    Reference Manual describes how to encode this parameter.

    WSMAXRATE is a DYNAMIC parameter.