[NTLUG:Discuss] Question about tape drives

[Steve Baker]

Kelledin wrote:

 > Magnetic tape media OTOH tends to lose data integrity
> over time, even if you lock it in a bulletproof, air-tight, 
> lead-lined vacuum chamber.

Years back, when the company I was working for did backups
to magnetic tape, they used to regularly fast-forward and
then rewind every tape they had in storage.  The reason
was 'print through' where the magnetic field due to the
bits on one length of tape would gradually magnetize the
loop of tape above and below it when wound onto the spool.

Rewinding the tape changes the precise alignment of one piece
of tape on the surrounding layers - changing the print through
from a coherent bit pattern that would easily corrupt the tape
to a more diffuse, randomized effect.

The tapes still degrade gradually due to print through - but
rewinding them regularly increases their life substantially.

Our magnetic backup stores were rewound at (IIRC) monthly
intervals.  The thing that finally forced them into looking
for more modern backup mechanism was when it took them
more than a month to perform the monthly rewinding regimen!

If you find this unlikely, you can prove it to yourself with
a very simple experiment.  Take out the oldest audio
cassette you own (preferably one you havn't listened to
in years) - and listen to supposedly silent gap before the start
of one of the audio tracks with the volume turned way up.

You'll hear a slight 'pre-echo' of the song starting a half
second before it actually does.  The delay is equal to one
revolution of the tape spool and the cause is print-through.

If you have audio tapes that you are greatly attached to -
sample them onto your PC ASAP and write them to CD's.
---------------------------- Steve Baker -------------------------
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