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by ChuckMcM
2363 days ago
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FWIW the failure mode (which was also common in drives for the SPARCStation at the time) was called "stiction." That occurred when the drive parked the heads, after power down, into the landing zone on the platter. At Sun we took apart a number of failed drives (which could also be recovered sometimes by giving them a sharp twist) and hunted for the root cause. The answer was that over some time the drive heads became smoother and the surface of the landing zone also became smoother. When the tiny edges of the head had been removed by this process, the surface of the head was pretty much optically smooth (very little variation) and when it landed in a part of the landing zone that was similarly smooth the surfaces would push out the air between them and become stuck just by air pressure and surface friction (stiction). The drive would not spin up until the head had lifted off the surface. The firmware issue was that head lift off was checked for so quickly that the power up of the spindle was aborted before anything happened (this was to prevent damage to the head by dragging it along the platter's landing zone). By jostling the drive you could manually cause the platters to rotate and if you found a spot that wasn't completely smooth (or if you managed to have the heads move out of the landing zone) the surface would be rough enough that the head wasn't being held down and it could lift off again. Seagate gave us a firmware fix which basically waited longer for the heads to lift off allowing the spindle motor to move the platter a bit before giving up. Quantum (the other disk supplier) beefed up the retract solenoid and gave us firmware that would try 'regular' retract and then 'heavy' retract before giving up. For a pretty long time I had a Seagate drive that had been disassembled to the point of exposing the heads and platters so that the effect could be demonstrated to skeptical engineers. |
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