Re: Old Magnetic Tapes

From: Alan Adams (alan.adams_at_orchard-way.freeserve.co.uk)
Date: 12/17/03 

Date: Wed, 17 Dec 2003 17:10:37 GMT

In message <oin0uvko41924ri9o5avq54q1ih0iov6ul@4ax.com>
          John Laird <nospam@laird-towers.org.uk> wrote:

> On 16 Dec 2003 08:06:22 -0800, s.stickle@asee.org (Sean Stickle) wrote:
>
> >I have three old magnetic tapes (from 1979) that have data we'd like
> >to read off. They show as having been created on a DEC PDP-11/70 and
> >copied to tape using PIP.
> >
> >Is there anyone about with a still functioning system that can read
> >such things?
>
> Folklore has it that you often get one chance, and one chance only, to read
> ancient tapes, as enough oxide falls off on the first read pass to render
> the rest useless. A data recovery company may be your best bet.
>

The last three months of my previous employment were spent attempting to
recover the data from our archive tapes. They were 6250bpi, written in the
main on TA78s, with two usable copies of each tape. (The third copy had been
stored in an unheated Portakabin, and I didn't want to use them.)

I was using Saveset Manager to copy to disk, then copied to DLT using the
same software.

I found that the first pass would read about half way through the tape, then
the oxide build-up made the tape unreadable. A repeat run would go further,
as the loose oxide had now been removed from the first half. With three
passes, most of the data was recovered. The tapes were mostly 12 to 15 years
old.

All data from all passes was kept, and merged afterwards. This was because
files successfully read on pass one could become unreadable on pass 2.

I also found that the tape usually stuck solidly to the head just after the
last file on the tape. This is because that part of the tape had never been
written. The rest had had, generally one, pass of the head when it was
created, and this removed a lot of loose oxide. It was normal to have to
clean the heads after writing a new tape.

I did all this recovery on a TSZ(05?) drive, and found it useful to disable the
lid sensor, so I could open the lid after each failure, then clean the heads
and continue from where the failure occurred, effectively making the
operation single pass.

Alan 

-- 
Alan Adams
alan.adams@orchard-way.freeserve.co.uk
http://www.nckc.org.uk/

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