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

    RMS_DFMBFSMT establishes the default RMS multibuffer count for
    magnetic tape operations. This value defines the number of I/O
    buffers that RMS allocates for magnetic tape files.

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

    RMS_DFMBFSMT is an AUTOGEN and DYNAMIC parameter.