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

    On VAX systems, SCSBUFFCNT is the number of buffer descriptors
    configured for all SCA. If an SCA device is not configured on
    your system, this parameter is ignored. Generally speaking, each
    data transfer needs a buffer descriptor and thus the number of
    buffer descriptors can be a limit on the number of possible
    simultaneous I/Os. Various performance monitors report when
    a system is out of buffer descriptors for a given workload
    which is an indication that a larger value for SCSBUFFCNT is
    worth considering. Note that AUTOGEN provides feedback for this
    parameter on VAX systems only.

    On Alpha systems, the SCS buffers are allocated as needed, and
    SCSBUFFCNT is reserved for Compaq use only.

    SCSBUFFCNT has the AUTOGEN, FEEDBACK, and GEN attributes.