/READAHEAD
       /NOREADAHEAD

    When a disk read is required to fill a cache lock, specifies that
    the read should be from the first block requested to the end of
    the bucket boundary. Readahead can speed up sequential operations
    by pre-loading disk blocks that are needed into the cache.

    If both /READAHEAD and /READBEHIND are specified, any block
    requested within a cache bucket causes the entire bucket range
    of blocks to be read into the cache.