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

    RMS_DFMBFSDK establishes the default RMS multibuffer count for
    sequential disk operations. This value defines the number of I/O
    buffers that RMS allocates for sequential disk files.

    The default value is usually adequate. However, if read-ahead
    or write-behind operations are used, a larger number improves
    performance.

    You can set this system parameter with the DCL command
    SET RMS_DEFAULT/SYSTEM and display the parameter with SHOW RMS_
    DEFAULT.

    RMS_DFMBFSDK is an AUTOGEN and DYNAMIC parameter.