On Tue, Oct 02, 2007 at 09:09:02AM -0400, Goslin, Paul wrote:
> Once Networker re-writes the label on the tape, I don't think any of the
> 'residual' data that may exist on it is recoverable since now the index
> to what was on the tape has been purged from Networkers database ..... 

It would certainly be tedious to find a random piece of data if you had
no index to it, but not impossible.

In all liklihood, you're backing up the catalog.  So older copies of the
catalog would have the index location prior to recycling.   

Much of this is not "can you recover?", but "how much does it cost to
recover?".  With a large budget, you can do a lot.

> Per the laws of physics - ANY magnetic media can be degaussed - it's a
> physical scrambling of the magnetic patterns on the magnetic tape
> emulsion coating.....

Yes.  I don't think the comment was about the impossibility of doing it,
but doing it to recycle the tape instead of destroying it.  The
statements I've seen are that a degaussed LTO tape is no longer
functional, so you might as well just destroy it in the first place.

>From the "magerasure" product manual:

  After being erased by Mag EraSURE, hard disks, removable disks and
  pre-formatted tape media (LTO, DLT and 3480/3490/3590 cartridges)
  cannot be reused or recovered. Please label and dispose of the erased
  media in accordance with local environmental standards.

> Put it next to any large AC motor (like on an HVAC
> blower) that has large coils with 60-HZ magnetic fields, and I'll bet
> you won't be able to read anything from any tape media...

I'm not so sure.  The denser the media, the higher coercitivity you need
to modify the domains.  I don't know what the field strength is next to
an AC motor (as close as I'm likely to get, anyway).  Is there a
resource that gives an average value?

> Like don't
> stand in a room with a CT scanner that's on  or all your credit cards in
> your wallet will get zapped also... 

I believe CT scanners are considerably more powerful, and the data on
card strips is much easier to modify.

-- 
Darren Dunham                                           ddunham AT taos DOT com
Senior Technical Consultant         TAOS            http://www.taos.com/
Got some Dr Pepper?                           San Francisco, CA bay area
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