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

    RMS_DFMBFIDX establishes the default RMS multibuffer count for
    indexed sequential disk operations. This value defines the number
    of I/O buffers that RMS allocates for each indexed file. For
    sequential access, a larger number that allows some of the index
    buckets to remain in memory can improve performance.

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

    RMS_DFMBFIDX is an AUTOGEN and DYNAMIC parameter.