Many years ago while on a service call at the Detroit
Free Press, I
witnessed a head crash
One of my first jobs was as a weekend operator for Tektronix' CDC Cyber
73 computer.
The machine was powered off at night. At around 9PM each night, the
entire system was powered down. Weekend operations started up a 8AM on
Saturday until 6PM, then Sunday from 9AM until 6PM.
When I'd come in, the machine was turned off, and I had to go through
the long rows of CDC "washing machine" type disk drives and power them
up one at a time. Couldn't power up more than one at a time, as the
surge load would cause breakers to pop, and that was definitely not a
good thing as a drive is spinning up. I'd have to hit the power on the
drive, and wait about 45 seconds for the drive to spin up enough that
the main surge was over with before I could hit the power switch for the
next drive.
It was New Year's Day (don't remember the exact year..probably late
'70's...maybe 1978). It was a Saturday or Sunday, can't remember for
sure. Anyway, I came in and started the power up routine. I had
powered up four or five of the drives when suddenly, the first drive
that I'd powered up started making a very strange shrieking noise,
followed very quickly by a very loud BANG!, then what sounded like the
aftermath of an auto accident. I looked back at the drive (I was perhaps
6 feet from it when this happened), and it was engulfed in a cloud of
smoke. Immediately thereafter, the klaxon went off indicating that a
Halon dump was imminent. I didn't know if the smoke was from something
on fire in the drive, or just from the headcrash, so I bolted out of the
room as fast as I could and let the Halon dump. I didn't want to take
the chance that there was a fire, and have it spread. When the Halon
dumped, the fire system automatically contacted the fire station that
was next door to the Tektronix campus. I waited outside the room until
the firemen showed up, less than 2 minutes from when the Halon dumped.
They went in with respirators and checked to make sure that there was no
fire. Everything was OK, although the area around the disk drive had
small shards of a metallic substance on the floor. They set up fans and
aired out the room. I was then able to go back in. My Lord, what a
mess. It appeared that the disk pack suffered a catastrophic failure.
Don't know if it was because of a head crash, bearing failure, or simply
a pack failure. Whatever it was, it completely destroyed the drive.
The CDC drive (can't remember the model number, unfortunately) was very
well-built. The enclosure for the pack was a huge metal casting with
very thick walls, acting as a scattershield for the pack. The shards
of metal around the drive were not from the pack, but apparently from
the motor, which stopped very violently and broke its mounts. The pack
was reduced to bits, which were all contained within the drive
enclosure. The smoked Plexiglas window in the lid of the drive that
allowed a view of the pack looked like it had been shot with a shotgun,
but didn't break. It was very thick Plexiglas.
I called our CDC rep -- we had two onsite engineers that were devoted to
the support of our system. Come to think of it, it was a Sunday (so it
had to be 1978), because one of them was at church and couldn't be
reached, though he was paged. I also called my boss, who had partied
the night before as a result of the New Year's holiday. He said to hold
off trying to do anything until he got there. After about an hour, one
of the CDC guys showed up, followed shortly thereafter by my boss, who
looked a little worse for the wear :-). The CDC tech. removed the drive
from the chain, cleaned up the mess, and made sure that
the other drives
were OK. The drive that failed had the boot pack on it, so we had
to
change the switch-based boot program (an array of toggle switches that
contained the PPU code to coldstart the machine from tape, which then
read in a disk book loader to boot from disk), and mount a backup boot
pack on one of the other drives. We were able to bring up the system
just fine, and do normal operations for the day. Later in the day, a
replacement disk drive was received, the system downed, the new drive
put in place, and we resumed normal operation. According to the CDC
rep., the failed drive was a total loss.
Thank God that the drives were so well-built. I can't imagine what
would have happened to me if pieces flew out of containment. I always
had a lot more respect for these drives after that event.
Rick Bensene