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    SubjectRe: Benefits from computing physical IDE disk geometry?
    On Sad, 2003-04-12 at 23:46, Timothy Miller wrote:
    > Any good SCSI drive knows the physical geometry of the disk and can
    > therefore optimally schedule reads and writes. Although necessary features,
    > like read queueing, are also available in the current SATA spec, I'm not
    > sure most drives will implement it, at least not very well.

    Some of them are in recent PATA and Jens Axboe implemented the TCQ for
    IDE, but its all a bit limited right now

    > So, what if one were to write a program which would perform a bunch of
    > seek-time tests to estimate an IDE disk's physical geometry? It could then
    > make that information available to the kernel to use to reorder accesses
    > more optimally.

    Its a common misconception that a disk looks something like it did 15
    years ago. Your ATA disk is basically an entire standalone computer
    running a small OS. The physical disk layout does not divide neatly
    into equal sized cylinders and some blocks may even be in suprising
    places due to bad block sparing or anything else the drive manufacturer
    felt appropriate.

    The drive firmware will look after a lot of the optimising for you,
    and once it gets TCQ it will probably get you all you want from SCSI
    with SATA. Until then playing games with it isnt likely to help - feed
    IDE disks large, sequential I/O as much as possible and they'll deliver
    you very nice numbers.


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