ronjhawk...@sbcglobal.net (Ron Hawkins) writes: > I'm afraid sequential pre-fetch kinda of makes your point invalid for > sequential IO.
when ibm first came out with full-track cache (3880-13/sheriff) ... it advertised a 90% hit rate ... based on 3380 track, 10 records per track and sequential read, where first sequently read on track would fetch the full track ... and then the next 9 sequential reads would already be in cache. however, if the application when to full-track buffering ... the same exact application and data would go from 90% hit ratio to zero percent hit ratio (effectively each track would be read as a whole, streamed through the 3880-13 cache right into processor memory ... and then would have any additional cache reference for the track). double "full-track" buffering would then overlap retrieval of the following track with the processing of the records in the previous track (masking disk retrieval latency, aka akin to instruction execution with prefetch &/or out-of-order execution to mask processor cache miss latency). -- virtualization experience starting Jan1968, online at home since Mar1970 ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@bama.ua.edu with the message: INFO IBM-MAIN
