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Can I erase sensitive data on an old hard drive with Neodymium Magnets?

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Re: Can I erase sensitive data on an old hard drive with Neodymium Magnets?

#111

Post by EvanAnderson »

linkmotif wrote: post #94
EvanAnderson wrote: post #17

Here's my anecdote: In 2006, while sitting at my desk playing a video on the hard disk drive of my Thinkpad T22, I held a single neodymium magnet (harvested from an old hard disk drive) about 6 inches from the left side of the unit (where the ~40GB-ish Travelstar 2.5" PATA disk was located). The video froze, Windows XP blue-screened, and the hard disk drive started emitting a ~10Khz whine. I jerked my hand away from…

Why wouldn’t they send you the image??

It was around Christmas, and a lot of people seemed to be out of the office for vacation. My sales rep was not technical and didn't understand what I meant when I asked for the "bitstream image" or "raw image" of the drive. I kept pressing, leaving voicemails in which I said stuff like "Look-- you don't know what I'm asking for. Send this to somebody in your engineering department and they'll know what I mean. I want to give you more money than you're asking for to get this."

Eventually I got a call back from somebody saying that they understood what I was asking for but couldn't send it to me. At that point I got fed-up and paid the minimum bench fee and asked for my disk back. I probably should have pushed the issue further, but my need was timely and I'd already started reconstructing the data from other sources.

Re: Can I erase sensitive data on an old hard drive with Neodymium Magnets?

#112

Post by EvanAnderson »

Waterluvian wrote: post #68
dpedu wrote: post #32

Earlier quoted context omitted.

From 6 inches away? Unless this was a hockey-puck sized magnet I'm calling it a coincidence. > (harvested from an old hard disk drive) Okay, this is making even less sense. "Hard drive magnets", in a drive, are millimeters from the spinning platters. I refuse to believe that the same magnet, moved 6 inches away from the computer caused catastrophic damage.

I stack hard drives and they keep working.

Absolutely. Hard disk drives don't stick to your refrigerator (like a naked magnet does) either. My layman's guess would be that the fields generated by the magnets in opposition in the voice coil are somehow "balanced", so that the net magnetic field produced by the drive is negligible.

Re: Can I erase sensitive data on an old hard drive with Neodymium Magnets?

#113

Post by quickben »

harshreality wrote: post #108
quickben wrote: post #92

Earlier quoted context omitted.

No, what he is saying, is that moving magnetic field, induces current , and can mess up the cheap power supply and/or other components, which can then mess up the drives. In a server, the power supply is on the other end of the chasis. In a laptop, it's a lot closer to the internals. > I don't buy that either. Theory: https://en.wikipedia.org/wiki/Electromagnetic_induction The forward model: https://www.youtube.com/w…

Nobody is suggesting that electromagnetic theory is false. The question is whether there's really a danger from HDD magnets in motion relative to nearby electronics or HDD platters. - HDDs often live right next to each other (separation of roughly 1cm, front to back). - Power supplies and their induction coils are right next to the drives in some cases, including for instance consumer grade NAS boxes. - HDDs tend to…

The magnetic head that writes to the disk, is fairly small and close to the platter. The flux is very contained. So that part seems negligible in the overall scheme of things.

Re: Can I erase sensitive data on an old hard drive with Neodymium Magnets?

#114

Post by quickben »

ars wrote: post #95
quickben wrote: post #92

Earlier quoted context omitted.

No, what he is saying, is that moving magnetic field, induces current , and can mess up the cheap power supply and/or other components, which can then mess up the drives. In a server, the power supply is on the other end of the chasis. In a laptop, it's a lot closer to the internals. > I don't buy that either. Theory: https://en.wikipedia.org/wiki/Electromagnetic_induction The forward model: https://www.youtube.com/w…

Do you understand what you are saying? A person, moving a magnet near a single wire - not even a coil - is going to induce utterly insignificant amounts of electricity. You'd need lab equipment to even detect it. It will do absolutely nothing whatsoever to computer electronics.

Open a powesupply before your next reply.

Re: Can I erase sensitive data on an old hard drive with Neodymium Magnets?

#115

Post by Turing_Machine »

tscs37 wrote: post #100
Turing_Machine wrote: post #99

Earlier quoted context omitted.

A hard drive has orders of magnitude less mass than an engine block. There's going to be nothing left of a drive but a puddle of molten metal after it's had a thermite grenade burn on it.

If you check research related to this and the DEFCON talk where somebody actually put thermite into the drive, there won't be a puddle of molten metal. You can put thermite on it once you burned the parts if you want.

The DEFCON guy used 15 grams of thermite. An AN-M14 TH3 incendiary grenade contains ~750 grams of thermite (technically thermate). Those are two different things. Entirely.

Re: Can I erase sensitive data on an old hard drive with Neodymium Magnets?

#116

Post by ars »

quickben wrote: post #114
ars wrote: post #95

Earlier quoted context omitted.

Do you understand what you are saying? A person, moving a magnet near a single wire - not even a coil - is going to induce utterly insignificant amounts of electricity. You'd need lab equipment to even detect it. It will do absolutely nothing whatsoever to computer electronics.

Open a powesupply before your next reply.

What am I supposed to reply to?

Instead, why don't you take a multimeter and see if you can measure any voltage (never mind current) by moving a magnet, by hand, near a single non-coiled wire.

Re: Can I erase sensitive data on an old hard drive with Neodymium Magnets?

#117

Post by Turing_Machine »

Turing_Machine wrote: post #115
tscs37 wrote: post #100

Earlier quoted context omitted.

If you check research related to this and the DEFCON talk where somebody actually put thermite into the drive, there won't be a puddle of molten metal. You can put thermite on it once you burned the parts if you want.

The DEFCON guy used 15 grams of thermite. An AN-M14 TH3 incendiary grenade contains ~750 grams of thermite (technically thermate). Those are two different things. Entirely.

Here's what 1 kg of thermite does to a hard drive:

https://www.youtube.com/watch?v=3lnqeodIIUw

I'm comfortable that the Curie temperature has been exceeded for all of those platters. :-)

Re: Can I erase sensitive data on an old hard drive with Neodymium Magnets?

#118

Post by dpedu »

ars wrote: post #96
dpedu wrote: post #32

Earlier quoted context omitted.

From 6 inches away? Unless this was a hockey-puck sized magnet I'm calling it a coincidence. > (harvested from an old hard disk drive) Okay, this is making even less sense. "Hard drive magnets", in a drive, are millimeters from the spinning platters. I refuse to believe that the same magnet, moved 6 inches away from the computer caused catastrophic damage.

I agree that it makes no sense. A magnet outside the case is not going to do anything to the platters. kees99 posted a possible explanation, where the magnet moves the voice coil, which ends up destroying the drive by writing data in the wrong places.

This can't happen either. Early hard drives (and I mean early: the 80s) needed precise head alignment (in respect to the how far the head is from the center of the platter) in order to read or write data in the correct location. If you've heard of "low-level" formatting, that's when a on-platter layout unique to the head and head movement mechanisms of the host drive is created.

Modern drives, however, are designed to "follow" the tracks that are cookie-cutter imprinted onto the platters. We use this design now as it's far easier to design a head that reads tracks and makes slight adjustments to stay on track, vs a head that needs to move to an absolute exact position.

In other words, modern drives are designed to combat this exact problem.

Re: Can I erase sensitive data on an old hard drive with Neodymium Magnets?

#119

Post by tscs37 »

Turing_Machine wrote: post #115
tscs37 wrote: post #100

Earlier quoted context omitted.

If you check research related to this and the DEFCON talk where somebody actually put thermite into the drive, there won't be a puddle of molten metal. You can put thermite on it once you burned the parts if you want.

The DEFCON guy used 15 grams of thermite. An AN-M14 TH3 incendiary grenade contains ~750 grams of thermite (technically thermate). Those are two different things. Entirely.

Good luck getting that into a datacenter.

Re: Can I erase sensitive data on an old hard drive with Neodymium Magnets?

#120

Post by [deleted] »

tscs37 wrote: post #119
Turing_Machine wrote: post #115

Earlier quoted context omitted.

The DEFCON guy used 15 grams of thermite. An AN-M14 TH3 incendiary grenade contains ~750 grams of thermite (technically thermate). Those are two different things. Entirely.

Good luck getting that into a datacenter.

[deleted]
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