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

       /CACHE_SIZE=buckets

    Specifies the number of indexed file buckets that are retained
    by in-memory cache during a recovery operation. Use the /CACHE_
    SIZE qualifier to set the size of a cache in order to improve
    performance when recovering indexed files. In general, the
    performance of the recovery operation improves as the cache size
    grows larger. However, other system considerations could affect
    the ideal size.

    The /CACHE_SIZE qualifier is similar in concept to the
    multibuffer count field (RAB$B_MBF) in RMS. For more information
    on how to tune your application using this value, see the Guide
    to OpenVMS File Applications and the OpenVMS Record Management
    Services Reference Manual.

    The /CACHE_SIZE qualifier applies only to indexed files. You can
    use this qualifier with either /BACKWARD or /FORWARD recovery.