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    SubjectRe: "Elevator ordering" and other oddities
    On Fri, 9 Aug 1996, Rakesh Dubey wrote:

    > >
    > > Sorry for the interruption, but there's some really excellent
    > > information coming out of the I/O scheduling discussions. Problem is
    > > that I don't understand a lot of it.
    > >
    > > Can anyone point me to a good "newless cluebie" introduction to, at
    > > the least, the terminology. I've no formal CS training (high school
    > > doesn't count), but I'm reasonably familiar with the kernel internals.
    > >
    > > Again, thanks.
    > I believe that "The Design of BSD 4.3" has some details on elevator
    > algorithm for ordering disk accesses.
    > The real idea is simple and uses the fact that it takes considerably
    > more time to position the disk head than to actually transfer the
    > data. So if we can minumize disk head movements we would save
    > time. Now look at a stream of I/O requests and reorder it so that the
    > accesses are towards the center of the disk (i.e. decreasing cylinder
    > number) and then after a point towards the periphery of the disk. In
    > order, you go up and then down.

    I think you just described saw tooth ...

    > -Rakesh
    PGP key pass phrase forgotten, \ Overload -- core meltdown sequence
    again :( and I don't care ;) | initiated.
    / This space is intentionally left
    | blank, apart from this text ;-)

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