OT: Curious hard disk behavior...

I've been going through a large number of secondhand hard drives. There are
three reasons to do this--properly remove the data with overwriting,
re-certify them for use and (eventually) re-use them.

As you can imagine, I've seen everything from drives that worked great to
dead ones. But I've also seen a few that did something interesting--at some
point in their past, one of the SMART monitored parameters (read error rate)
dropped to the lowest possible value. At this point in time, however, these
drives have all returned that value to a "perfect" level.

I thought I had a good explanation for the first drive that showed this
behavior--it had been in a system where the cooling fan in the power supply
failed. It ran this way for a long time before the power supply finally
burned out. The bearings in the drive's spindle motor were very loud. I
figured that it had simply gotten hot enough when running to affect the
magnetic stability of the disk platters. It had also run out of spare
sectors to remap.

The other two drives are in much better shape--both of them operate quietly
and quickly. I don't think they ever got too hot or anything like that,
which would seem to invalidate the "heat" theory I'd come up with to explain
the first drive's "bad experience".

Any ideas? The first drive was definitely dying, but the other two seem to
be in top-flight shape. I've beaten on them pretty hard and haven't had them
fail.

William


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