Sunday, 15 December 2013

More on magic finger

Speaking of which ...

We were very busy that afternoon in the data recovery room, lots of work had come in, and we were working our way through a queue of cases.

In came a customer, looking desperate. "I need a data recovery, and I need it quickly," he said, or words to that effect. Barry and I looked at each other; we were both in the middle of doing a DR, and you can't really break off one DR to do another, because the drive you're working on might fail totally at any time, and then you wish you hadn't.

I told the customer to sit and wait; I was applying magic finger at the time, and watching the data stream off the drive onto the Bernoulli Box, which was how we stored it for replacing on diskettes later.

So he was sitting doing nothing, and I wasn't doing very much either, just sitting there with my finger in exactly the right place, and when the stream of data faltered, moving it slightly until it resumed.

I should explain how magic finger worked. The ST225 was a couple of spinning platters, and the head moved in and out, driven by a stepper motor and connected via a couple of metal bands. The way this failed, was that the metal bands strertched slightly, so that the head wasn't exactly on track. But the spindle of the stepper motor came through to the outside of the drive, you could put your finger on it. And by pressing slightly, and twisting slightly, you could make a very small change to the position of the heads on the platters. And you could get the heads on-track.

There was a program we ran, called lecopy, which did a sector-by-sector copy from the drive to the Bernoulli Box, and it showed you the sector numbers as it went. If it couldn't read a sector, it would retry a large number of times. So if the head was off-track, the display stopped at a sector number, but when you applied magic finger, the stream of data (and the stream of numbers) would resume when you got it right.

So I was sitting, not really doing much, just watching the numbers and occasionally wiggling my finger, and the cusomer was sitting watching me, looking twitchy.

And I had an idea.

"Look," I said, "if you could sit here, and put your finger just here, and watch the numbers go by, and press and wiggle your finger if the numbers stop ... then I could start on your data recovery right now."

He was very happy to agree. So he sat there for me, doing magic finger (and I didn't actually explain to him that he was doing a data recovery for another customer), while I took his drive to another part of the DR room, and used the windmill technique, which worked a treat, and he was a very happy bunny.

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