From: timhu@ico.isc.com (Timothy Hu)
Subject: Re: dc2120 tape cartridge error rate
Organization: Interactive Systems Corp., Boulder CO
Date: Sun, 10 Jan 1993 06:33:45 GMT

Someone emailed me a tape question:

> I currently own a CMS Jumbo 250.  Recently, I saved about 50 megs on a tape
> cartridge and left for vacation.  With the sudden cold front on the West
> Coast, the tape I suspect underwent some temperature change (probably greater
> than 20 degrees).  When I tried to store more infomration on the tape, I
> get an error rate of 200+ fixable errors per 5 megs.  My question is this:
> was the temperature change responsible for these errors?  If so, is there
> any way to reliable get the 50 megs (i.e. some sort of heat solution or
> something) back?

And here is my reply:

3M recommends that you retension the tape when it is subjected to a wild
temperature swing. This temperature swing is defined as 30 degrees F or
more. This brings to mind an experience I had whilst in Japan on some
business. I had packed with me an extra set of operating system tapes
(in addition to the tapes that were shipped with the Sun SPARCStation
two weeks earlier). Well, when it came time to install the OS, the tapes
shipped with the system would not load because of a read error. Since the
tapes were written in a simple format (tar, cpio, dump -- i forgot which
format), there was no error correction facility to assist in recovering
the data on the tape. Thus, upon reaching the first error, the install
procedure aborted. I tried again, again, and again to no avail. I
thought that I could just pull out the backups that I had brought with me
on the airplane and just load those. Guess what? Same problem. One thing
you notice about Japan is that the island is *very* humid and that they make
little or no attempt at lowering it in their offices (via air
conditioning). Let's look at the facts:

1. The tapes that were shipped with the system two weeks prior to my
arrival went by boat. Thus, they were subjected to two weeks of "boat"
conditions -- high humidity and maybe even temperature extremes.

2. The "boat" tapes sat in the humid Japanese climate days (with
the computer) before my arrival

3. The tapes that I had brought with me spent two days in the Japanese
climate in my briefcase.

4. I did not retension any of the tapes before I used them.

The SPARCStations did not have a facility to retension the tapes (the OS
wasn't loaded yet). Fortunately, I had set the computer up in an
environmentally controlled room where I could bring the humidity down.
Also, there was an SGI in the next room that was working. I decided to
retension the tapes in the SGI tape drive. While the tapes were
retensioning, I brought the temp and humidity down in the lab. I loaded
the tapes one more time, and BAM! it worked. This whole fiasco took seven
hours. I don't know if the temperature swing or humidity (or both)
affected the tapes.

Yes, I was sweating bullets. If the OS installation didn't work, I
couldn't continue with anything else (seven days' worth of work).

There are several lessons that can be learned from this:

- keep your tapes away from temperature and humidity extremes

- if you can do it, have more than one backup of critical items (the
copy I had brought with me saved my b*tt) as the first copy completely
failed

- if you suspect that your tapes have been subjected to extreme
conditions (see the literature that came with your tapes), let them
acclimate to normal room temperature for an hour and then retension them
before you attempt to read or write to them.

	Just a note here on extreme conditions. 3M tapes are
	"comfortable" at 41F to 113F. If your tapes have been sitting
	at, say, 50F and then get exposed to 100F (both are within
	the tapes' "comfortable" range), you should retension them
	because they have experienced a pretty severe temperature
	swing.

- you may have to retension more than once. I had to do it five or six
times. I don't know why this is. Maybe this helped the tape to acclimate
faster as this moved the tape around?

- if you're not travelling alone, make another copy of the items and
give the tapes to your traveling companion(s).

Other lessons I learned:

- do NOT walk through a metal detector with your tapes. They
use a magnetic field to detect metal objects.

- do NOT XRAY them. I know that airport xray machines are supposed to have
minimal magnetic fields, but what if a machine was improperly maintained
or malfunctioning or the tapes you're using are marginal? Have them
manually inspected. It will only slightly delay you and it's cheap
insurance.

All the above also applies to floppies and hard disks (except for
retensioning. I don't know how to retension a disk :-) ).

Tim
-- 
Timothy Hu timhu@ico.isc.com	 | The intelligence (or lack of) expressed
Interactive Systems Corporation  | above does not necessarily reflect the
Resource Solutions International | that of anyone else.
Newsgroups: comp.sys.ibm.pc.hardware