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Comment by azinman2 | Hacker News Reader

How did the data not get destroyed by the magnet?

It's changing magnetic fields that wipe HDDs. Such as powerful electromagnets.

In a clean (enough) room, they could have opened the drive, and just poked the actuator arm.

Decades ago, I had a HDD that wouldn't spin up unless I nudged the platter with a pencil erasor. Very near the center, of course. There was a hole in the case, in just the right place, with Al tape over it.

Doesn't even have to be a very clean room... I played around with an old 1 gig drive years ago. My friends and I opened up the case so we could watch the drive doing it's thing. We did a fresh os install and watched as it formatted the disk and copied files. The head was remarkably strong, and would move so fast it looked like it was in 2 places at once while copying files. It was fun to stick a screwdriver between the 2 ghostly write arms, and have the screwdriver almost knocked from your hand, while the drive went on like nothing had happened. It ran for weeks before it died.

I've also stuck a 3 1/4" floppy disk to a huge 2"x2"x5" neodimium magnet with no ill effects. The drive was able to read it fine afterwards with the same md5 hash of the contents.

I'd say it needs to be pretty clean. Back in the day it was a thing to remove the hard-drive cover and replace it with plexiglass. Once densities got to around 100 GB (don't remember the specifics but somewhere around 100 */2) it turned out that noone was successful with even momentarily open the drive chassi without ruining some part of the platter due to dust.

My first HDD has a 540MB drive, I ran DOS. Eventually I upgraded to newer computers, and I opened the old drive, and put in on the wall on display. It stood there for at least a decade, possible 15 years, before I moved to a different country. Before leaving, I decided to connect the old drive to a computer, just for kicks.

Remarkably, I could read data off it. Not much, file i/o mostly ended up in failure, but I could at least see the file structure. I did not expect this.

That's very cool. Maybe I'll try it, just for lulz.

> I've also stuck a 3 1/4" floppy disk to a huge 2"x2"x5" neodimium magnet with no ill effects. The drive was able to read it fine afterwards with the same md5 hash of the contents.

Right.

But thinking of EvanAnderson's anecdote, maybe a permanent magnet near a spinning platter is a changing magnetic field, from the perspective of the platter surface.

Still, with the platter inside a steel case, you'd need a very strong permanent magnet, held very close.

That's pretty cool. I had a few old drives and on purpose took them apart. So far I was not able to duplicate what you were able to do (this was last month). I had an idea that it might work in some way. Glad that you can confirm it did at least when you tried.

If you videoed any of that, I'd love to watch it on youtube (or somewhere).

There are actually very powerful permanent magnets inside of every spinning hard drive already, so clearly there's more to destroying data than just having a magnet nearby.

https://www.kjmagnetics.com/blog.asp?p=hard-drive-destructio... has a writeup about trying and failing to wipe a drive with extremely powerful magnets.

There are degaussing devices that look like microwave ovens, and for all I know, that might be largely how they operate.

But outside of those, no magnet that you can hold in your hand will demagnetize a modern hard drive at any distance outside of the case, because there are magnets inside the case that are stronger than you can hold in your hands, and they’re used to move the head/arm assembly at mind-blowing speeds — and accuracy.

I have some old Imprimis Wren VII hard drive magnets still on my dad’s fridge, from the time when I did an internship there in 1989. I won’t say that you can’t remove them from the fridge, but they are stuck on there extremely well, and there are a number of people who had been injured by having their hand or fingers caught between those magnets and a ferrous metal object — like a fridge.

And that was 1989. The magnets they use now are much stronger.

Now, if you happened to put a hard drive inside an MRI machine, that would do the job. But then you’re also talking about a machine that could suck up a vacuum cleaner from across the room and turn it into a lethal projectile. A proper degausser will be a lot weaker than an MRI machine.

You know what is sad about a small business (kjmagnetics.com) that you linked to? They are exactly what will be killed off by Amazon. The small and knowledgeable specialty store very similar as I am sure many of us remembered happened to 'Stereo Stores' once the big boxes stores came along (or hardware stores). Nothing new about this of course just that with Amazon it's greatly accelerated.

Amazon is 8 years older than K&J Magnetics...but sure

What does that have to do with the point that I am making? Did I make say it started before Amazon?

Yeah, this technique should really only be used if, and only if, you need the drive itself to be fixed and no longer care about the contents of the drive (e.g. if it was in a RAID 1 and manually cleared afterwards).

the whole magnet and hard drives thing is a really old hoax. with normal household magnets or even strong neodym magnets nothing will happen to your data but if you have a really strong industrial electro magnet at hand you can wipe a drive with it...

here is an old national geographics video on the topic https://www.youtube.com/watch?v=U8LWTe5CqQg

Here's my anecdote:

In 2006, while sitting at my desk playing a video on the Travelstar 40GB PATA drive in 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 ~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 the PC immediately when the whine started

BIOS would no longer detect the disk on that machine, or any other I tried it on (on both USB-to-PATA and honest-to-goodness motherboard PATA controllers). The drive spun up but made a repeated ticking sound (I assume seeking back and forth looking for servo tracks).

I sent the drive to Kroll Ontrack (because, stupidly, I had billing data that wasn't backed-up on the drive). The report I received back indicated that 80% of the drive's sectors were unreadable.

As an aside: The data I was looking for was ASCII text and Kroll Ontrack was completely unhelpful in just sending me a bitstream image of the drive so I could grovel thru looking for data I needed. Being plain ASCII, their "file carving" tools didn't locate any of the data. (They sent me a "preview" of the data they'd located, and while it got lots of Microsoft Office-format files, it didn't have any ASCII text files). I offered them a 3x multiple of the rate they asked for file-level recovery to simply send me the bitstream image of the disk that they'd already made. They wouldn't do it, and wouldn't even let me pay to talk to somebody who understood what I was asking for. I ended up taking a major loss on the billing data I destroyed. I'll never recommend them to anybody.

I won't ever play with neodymium magnets around spinning rust media again either. I also had a major failure of my discipline re: backup at that time, too. The cobbler's children always go barefoot-- I was being too cavalier with my backup strategy (or lack thereof) and not treating my own data like I would a Customer's.

> the hard disk drive started emitting a ~10Khz whine

This sounds like the head crashed and physically scraped the platter.

Sounds like a coincidence.

It does sound that way but, boy, it was eerily timed if it was.

I'd bet on related, but not what you thought. If I had to guess, I'd put my money on the magnet pulling some tiny metal bits into the control board and shorting it.

But one thing is for sure. OnTrack are dicks. Can confirm.

Magnetic field falls off with inverse cube of distance once you're past the approximate size of the magnet. Not to mention that the drive itself is in a ferrous enclosure that provides a lot of shielding... the magnetic field you applied at 6 inches is approximately nothing.

I will definitely concede that I may have the 6" measurement wrong. Heck-- I may have actually put my hand right on the PC.

I stack running hard disk drives, all of which have large neodymium magnets inside them, in close proximity all the time with no ill effects. It makes no sense.

Isn't it inverse square?

No. Magnetic fields fall off as 1/d when d is small compared to the size of the magnet, progressing to 1/d^3 when d is large compared to the magnet. (E.g. weird edge case-- it's inversely proportional to distance from an infinitely long wire).

Electromagnetic radiation from point sources falls off as 1/d^2.

Thanks a lot, both of you, learned something!

No, it’s a dipole moment instead of a monopole like electric charge. It goes as 1/r^3 in the far field.

Interesting one of the first 'tales' I read about was some person in (I think) Sweden who took his drives home in his car with heated seats. And when they needed to use them they wouldn't work. The point was 'you have to test backups'. Now that I am thinking of it possible this was even with tapes not hard drives.

By the way with that video I am also thinking maybe it wasn't the magnet that scrambled the drive but some other force that was applied as a result of the effect of the magnet on chips or the laptop. [1]

[1] I don't think that was what happened but the test does not isolate the drive from any other possible impact is my point.

It has to be an electromagnet. I remember doing this experiment with floppy disks and magnets for a middle school science fair. Normal magnets don't do a thing, but electromagnets can change data.

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