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2006-07-22

A voice of the reason from the distant past


Dedicated to VM and file system developers and researches...

It is immediately apparent from these figures that moving-arm disks should never be used, neither for paging applications nor for any other heavy-traffic auxiliary memory applications.
Peter J. Denning -- Virtual Memory.
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4 comments:

  1. Good luck finding a drum storage unit these days ;-)

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  2. I wonder why disks don't have more than one "moving arm". With native command queue SATA disks (and something similar surely existing in the SCSI world for a long time), you could get quite an improvement in seek time and throughput... Or not actually?

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  3. I wonder why disks don't have more than one "moving arm"
    In fact, some of them do. High-end IBM installations use "fixed-head disks", where each track has its own head. You may imaging the cost of it.

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  4. High-end IBM installations use "fixed-head disks", where each track has its own head.

    Well, this sound almost like the good old drum. And no, I really don't want to imagine the price of such a beast. ;-)

    I was actually thinking of just sticking an arm into each corner of the case of your average disk: four arms, quarter the average seek time, and up to four times the throughput (yeah, I know this is a misleadingly coarse upper bound). And it doesn't seem to be that much more arms and heads to make it cost insanely more. Though, frankly, I have no idea what are the expensive parts of a disk, and making a firmware to use those four arms really well may also be a bit tricky.

    -- crankyjack

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