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    SubjectRe: disk head scheduling
    On Fri, 19 Mar 1999, Ingo Molnar wrote:
    > On Thu, 18 Mar 1999, Yasushi Saito wrote:
    > > What I tried to implement was two-way elevator seeking (SCAN). In my
    > > tiny benchmark that let many threads write on random files, SCAN
    > > showed a throughput improvement of anywhere between 0 to 20%. But I
    > > also noticed benefits in the original algorithm (it's fairer), so I
    > > don't know if my change makes sense.
    >
    > the bigger problem is that dumber devices will just execute non-forwards
    > ordered requests. Most modern harddisks will either cache a full track, or
    > will reorder the request per-track anyway, but eg. a floppy disk or a
    > CD-ROM will execute the requests as given, and the 'downwards' queue will
    > perform badly. Would you mind doing the seek benchmark on your CDROM too,
    > just to test this theory?

    Well of course a 2-way elevator should sort by *ascending* sector within
    descending track. I take it this is difficult?

    --
    Mark H. Wood, Lead System Programmer mwood@IUPUI.Edu
    Specializing in unusual perspectives for more than twenty years.


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