VMS Help RECOVER, Qualifiers, /BI_BUFFER_SIZE  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /BI_BUFFER_SIZE=blocks

    Specifies the number of blocks that RMS recovery reads for each
    I/O from the journal. This qualifier is similar in concept to the
    multiblock count field (RAB$B_MBC) in RMS. The blocks parameter
    is the size of the buffer used to read the before-image journal.
    The parameter can takes values of 1 to 127 blocks.

    Use the /BI_BUFFER_SIZE qualifier to tune your application and
    improve performance during recovery. For more information on
    how to tune your application using this value, see the Designing
    Files/Units of Input/Output section in the Guide to OpenVMS File
    Applications and the OpenVMS Record Management Services Reference
    Manual.

    You can use the /BI_BUFFER_SIZE qualifier only when you specify
    the /BACKWARD qualifier.