Path: utzoo!attcan!uunet!lll-winken!lll-tis!ames!mailrus!cornell!uw-beaver!tektronix!teklds!amadeus.LA.TEK.COM!jamesa
From: jamesa@amadeus.LA.TEK.COM (James Akiyama)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Need a 60M to 80M hard disk for a *truck*
Message-ID: <3940@teklds.TEK.COM>
Date: 8 Sep 88 20:21:10 GMT
Sender: nobody@teklds.TEK.COM
Reply-To: jamesa@amadeus.LA.TEK.COM (James Akiyama)
Organization: Tektronix, Inc., Beaverton,  OR.
Lines: 66

Trying to use a hard disk in a truck would be a very challenging task.  There
are a few points you'll want to keep in mind.

First, the standard shock mounts on a hard disk (the rubber isolator between
the hard disk chassis and media chamber) are "tuned" for normal computer
environments.  This "tuning" involves increasing its resistant to higher
frequency (above about 20 Hz) vibration.  You will find that these shock mounts
generally decrease the hard disk's immunity to lower frequency shock.  This is
the reason most hard disks come packed in relatively snug fitting containers.
These containers are designed to purposely defeat the standard shock mounts.
If the standard shock mounts were not disabled, large displacement waves would
cause the media platter to "crash" into the chassis as the mounts run into
their maximum displacement.  The shock energy would then be dissipated in a
very short time (at the point of impact) rather than spread out over a longer
period.

Because of this, it will be necessary to mount the fixed disk in a shock
absorbing enclosure.  This enclosure should be tuned to dampen low frequency
vibrations.  The design is a complex interaction between the existing
shock mount and mass of the hard disk media chamber, and overall mass of the
hard disk (including chassis).

Alternately one could design a system where the manufacturer's shock mounts
were disabled (or removed).  This would void their warranty (although I think
your application would void their warranty anyway).  This would simplify the
design considerably by removing one of the potential resonant sources.

You will want to also use a 3 1/2" drive since these tend to offer better
shake and shock figures.

You would also want to consider using a plated media disk drive.  A voice coil
system with auto park and auto-lock would help if the drive is powered down
while the truck is moving.  Be sure the drive does lock--some use a spring
tension to pull the heads off the data surfaces.  These are much more likely to
come out of the parked position under high shock.  If the drive will be powered
up during this time, a stepper design may be preferred.  The "cogging" effects
of the stepper will help minimize sideways movement of the head assembly.  A
voice coil design offers very little resistance to such side-ways movement
while powered up.

When the system is in place you'll want to monitor the number of times the
computer re-calibrates the drive while running.  Excessive re-calibration while
running is a good sign that the drive is being subject to excessive shock
while running.

As far as drive recommendations, I would seriously look at the CDC (Control
Data Corporation) series of drives.  Best would be the CDC "Swift" 80 Meg
drive (although I'm not sure its available yet).  Unfortunately this drive is
not plated media--CDC doesn't use plated media except on their very high
capacity drives (> 100 Megs).  The drive is voice coil with a very fast (16.5
mS) average access time.  Note that the 80 MEG drive is currently the "bottom
of the line" in this series of drive (CDC tends to only come out with
"high-end" drives--at a price higher than most).

CDC also has a well-earned reputation of meeting their specifications in a
real-world environment as opposed to many other manufacturers who only meet
published specifications in their "laboratory-controlled environment."

Hope this helps, and good luck.

James E. Akiyama
jamesa@amadeus.LA.TEK.COM
UUCP: ....!tektronix!amadeus!jamesa
ARPA: jamesa%amadeus.LA.TEK.COM@RELAY.CS.NET

DISCLAIMER:  These view are my own and may not reflect those of Tektronix or
and affiliates.