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<p class="MsoNormal">Just as I would a series of emails about sewing spools, I’ve lost interest in this thread. :p<o:p></o:p></p>
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<p class="MsoNormal"><b>From:</b> Ale <ale-bounces@ale.org> <b>On Behalf Of </b>Jim Kinney via Ale<br>
<b>Sent:</b> Friday, April 12, 2019 8:17 AM<br>
<b>To:</b> Alex Carver <agcarver+ale@acarver.net>; Atlanta Linux Enthusiasts <ale@ale.org><br>
<b>Subject:</b> Re: [ale] destroy old drives<o:p></o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt">Heat above Curie point will always remove all data from all recovery methods.<o:p></o:p></p>
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<p class="MsoNormal">On April 12, 2019 1:22:49 AM EDT, Alex Carver <<a href="mailto:agcarver+ale@acarver.net">agcarver+ale@acarver.net</a>> wrote:<o:p></o:p></p>
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<pre>No, the magnetic strength of the head itself hasn't changed because<br>there's still a minimum field required to flip the domain of the<br>material which is intrinsic to the material coercivity. Instead the<br>head has changed technology from old wire-wound heads to metamaterials<br>that exhibit giant magnetoresistance. The head is now physically much<br>smaller so it can confine the field into a tiny area while avoiding some<br>of the divergence that can overwrite adjacent tracks. Remember that the<br>platter already has servo tracks buried within it which the drive does<br>follow to maintain positional tolerance so there's certainly more than<br>one layer of material present in the platter.<br><br>Even still, print through happens but it does take time. It's also not<br>necessary for the domains below the surface to fully align. The modern<br>hard drive is an exercise in digital signal processing more than using a<br>hysteretic circuit to detect the individual domains. The domains are so<br>small and traveling so fast past the head that it's actually an spread<br>spectrum RF signal being transmitted from the read head. Modern drives<br>don't read individual ones and zeros anymore, they read a waveform and<br>use statistical processing to recreate the bits on the other end.<br><br>The magnetic domain won't be fully erased with a basic rewriting<br>program, there will always be a residual field especially if those<br>particular domains are not rewritten very often. So it's not impossible<br>to do some additional DSP magic and deconvolve what is written on the<br>surface from what is deeper in the layer, information that will subtly<br>alter the waveform. We already rely on this technology in things like<br>the GPS system and other similar spread-spectrum/ultra-wideband devices.<br> A determined actor could filter out the strong surface signal and<br>eventually recreate a good portion of the underlying signal.<br><br>On 2019-04-11 14:09, Jim Kinney wrote:<o:p></o:p></pre>
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<pre>Really? The only groups that want the data _that_bad_ have subpeonas.<br>The other groups that can read around the holes already have your data.<br>All you're really trying to do is make sure the drive is not usable for<br>the basic computer bad guy.<br>As areal densities have increased exponentially from 10M drives to 10TB<br>drives in the same space, the size, and thus strength, of the magnetic<br>domains has decreased exponentially. So the bleed over has also<br>decreased. The transition to vertical magnetic domains has made the<br>crosstalk to the platter substrate nearly zero. Add in the platters are<br>simply not magnetizable at all and there's basically no data bits<br>anywhere possible except on the platter surface.<br>bad ascii art:<br>N-S bit domain on surface___ platter surface<br>S-N induced bit domain subsurface<br> N S | | 2 adjacent vertical domains 1<br>0 S N____ platter surface<br> N - S Induced data bits are just wrong! Now mix in the 2D spacial<br>arrangement and which subsurface pole pairs with which other? No<br>monopoles in magnetic media (yet :-)<br><br><br>On Thu, 2019-04-11 at 13:31 -0700, Alex Carver via Ale wrote:<o:p></o:p></pre>
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<pre>If someone really wants your data, holes don't matter. The rest of<br>theplatter is still intact in that case and can have the data<br>extracted.<br>There's also no guarantee that Dban can write enough to be sure that<br>themagnetic domains are fully randomized deep in the platter. The<br>longerdata sits statically on the disk the more opportunity for the<br>surfacedomain to imprint on deeper domains (this is actually a<br>problem withmagnetic tape, magnetic data can print through from one<br>layer of tape tothe next layer when it's wound on the spindle).<br>A serious entity can perform a deep level scan of the platter<br>andretrieve the low level signal under the surface domains and see<br>previousdata. The drive head typically isn't powerful enough to<br>write thatdeeply because it has to keep the tracks narrow.<br>On 2019-04-11 12:13, Steve Litt via Ale wrote:<o:p></o:p></pre>
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<pre>On Wed, 10 Apr 2019 22:11:42 -0400Jim Kinney <<a href="mailto:jim.kinney@gmail.com">jim.kinney@gmail.com</a>><br>wrote:<o:p></o:p></pre>
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<pre>Dban advantage: it can be done across hundreds or thousands of<br>drivesbefore larcenous third party "shredders" physically touch<br>the drives.<o:p></o:p></pre>
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<pre><br> That's a good point.<br> Doesn't dban take an hour or more? How many drives can I do with<br> onecomputer? How long would it take to test whether each is really<br> blank?<br> What might be nice with 1000 drives to do is dban followed by<br> drilling3 holes in each drive. I'd say each drive would take 1<br> minute for 3holes, so it's about 2 days for one employee to drill<br> the holes. Or,perhaps, one employee could both dban and drill the<br> holes, drilling theholes while the next batch is dbanning.<o:p></o:p></pre>
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<pre>_______________________________________________Ale mailing <br><a href="mailto:listAle@ale.org">listAle@ale.org</a><br><a href="https://mail.ale.org/mailman/listinfo/ale">https://mail.ale.org/mailman/listinfo/ale</a><br>See JOBS, ANNOUNCE and SCHOOLS lists at<br><a href="http://mail.ale.org/mailman/listinfo">http://mail.ale.org/mailman/listinfo</a><o:p></o:p></pre>
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-- <br>
Sent from my Android device with K-9 Mail. All tyopes are thumb related and reflect authenticity.<o:p></o:p></p>
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