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 the PC immediately when the whine started.<p>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).<p>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.<p>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 saying. I ended up taking a major loss on the billing data I destroyed. I'll never recommend them to anybody.<p>I won't ever play with neodymium magnets around spinning rust media again.
If you want to get rid of a harddrive with sensitive data I would first suggest that one gets familiar with the thought of not being able to sell it as used.<p>Personally for my drives, I use Boot and Nuke to erase the drive three times, first with zeroes, then with random data, then with zeroes again. After that I disassemble the drive, put a strong magnet over each platter, shredder the drive into almost powder, burn the pieces in a fire and then throw away the leftovers. Probably overkill but I want to be certain.
I worked in the HDD industry, doing signal processing for a few years. HDDs are pretty much magical. It's insane how delicate, yet robust it all is.<p>But to put things into perspective with some numbers, the write heads on a modern HDD use somewhere on the order of 50 mA of current. That may sound like a reasonable amount until you consider that the magnetic field [flux] is condensed down to a 60 x 20 nm area. It usually takes a little over 1 Tesla to flip the magnet.<p>I have been out of the Industry for a little bit now, but things are moving towards a magnetic substrate that has a smaller grain size (allowing smaller bits at a similar SNR) but a coercivity well over 3T at room temperature.
Hard disks are surprisingly hard to destroy on-demand. There was a DEF CON 23 talk [1] exploring ways to quickly wipe your servers in situ using physical methods.<p>[1] <a href="https://www.youtube.com/watch?v=-bpX8YvNg6Y" rel="nofollow">https://www.youtube.com/watch?v=-bpX8YvNg6Y</a>
I think magnets could compromise the read/write head, or other electronic on the drive. So why not just mulch the drive with a grinding service?<p>If you're looking to reuse the drive, use one of the NIST SP 800-88 Revision 1 recommendations. It lists the methods in the preferred order. Ideally the drive supports ATA crypto secure erase, where it just wipes the DEK and KEK, poof, in effect the crypto encoded form of you data can no longer be turned into plain text. You can mimic this with software FDE (Bitlocker, LUKS/dm-crypt, Filevault). Fast.<p>But they also say it's adequate to use the other kinds of secure erase, because other than firmware bugs/exploits it's the only way to erase sectors not assigned an LBA, e.g. sectors that once had an LBA, had data written to them, but subsequently failed overwrite and the LBA remapped to a reserve sector, leaving data on a sector that cannot be overwritten via SATA commands.
Here are few experiments with a 6 inch neodymium magnet with few devices:<p><a href="https://www.youtube.com/watch?v=_yEu2R1gYSs" rel="nofollow">https://www.youtube.com/watch?v=_yEu2R1gYSs</a><p><a href="https://www.youtube.com/watch?v=4l-6qWaZpVQ" rel="nofollow">https://www.youtube.com/watch?v=4l-6qWaZpVQ</a>
HIPAA - regulated health data requires physical destruction of retired hard drives. Usually this is done in sight of a video camera. The operator shows the drive's serial number to the camera and then drops it into the grinder.<p>CMS (Centers for Medicare and Medicaid Services) can require proof of destruction. That video does it.
This is exactly how I got out of a final project in middle school. Wiped my HDD with a Neodymium magnet right before the deadline and claimed my computer was "broken"... Of course this wasn't done for highly paranoid reasons where I needed to ensure the data was <i>really</i> all gone, but funny story nonetheless. People are more sympathetic when they think a computer "randomly" stopped working.
There are techniques used to recover previously erased information on HDDs. These techniques have been available since the 90's. The best way to make it unrecoverable is to melt the disks by the use of whatever techniques you have available, including ox-acetylene torches (the favoured method for the company at the time I was working for them), putting into a furnace (as suggest by others here), etc.<p>The problem with erasure is that there is residual amounts of magnetic fields that can be picked up by the right equipment. In the day, it was reported that they had success with recovery of information that had been overwritten by 8 - 10 times. It just took a lot of patience to do so. Those who want to recover this information will have that patience.
Is it really necessary to overwrite the data multiple times to erase it? With the densities provided by today's hard drives, the techniques you used to be able to use to get partially erased data are routinely used by the disk drive itself for normal reads.
When I had a few old hard drives to dispose of I drilled several holes in each one, through the case and platters, then filled them with water and left them outside for a few days so that anything that might rust would do so.
even if you drill a hole in the drive, data can still be recovered from it. anything that leaves large pieces of drive intact really isnt ideal. over the years i had collected dozens of platters from both myself and other people. for some reason, when i was younger i was obsessed with collecting hard drive magnets and also smart enough to understand that i probably shouldnt throw the platters away. so a few years ago i decided it was time to destroy all of these annoying platters that i have to worry about misplacing. i naturally assumed that it was going to be easy to find some kind of service, shredding or wiping, for hard drives or hard drive platters. there were no good options. so i tried smashing the platters into small pieces, and this worked for some of the thinner laptop hdd platters. one strong hit would break them into millions of tiny pieces. but most of them just bent or dented. and to thoroughly bend and dent the whole surface of all the platters would be super annoying. so i decided i should just melt them -- they are made of aluminum which has a low melting point. it was surprisingly easy. just get an old coffee can or better yet a stainless steel gas cylinder or even a ceramic crucible. they arent too expensive as far as i know. i used a can. then just surround the can with some bricks for insulation and apply a normal blow torch. set the torch down so it blows into the void between your vessel and the brick jacket. after the platters are melted you can even cast them into something, like a belt buckle. its all a bit silly, but it does feel nice to know that it is literally impossible for anyone to ever know what was on those platters.
Even if the test would have succeeded, this is a bad idea.<p>With a magnetic swipe card that you demagnetize so it is no longer read successfully, you may well be able to recover the information using a better reader.<p>Depending on drive age the same may be possible using a hard drive.<p>The best option for modern drives is still to use software to wipe the drive and if reuse is not required destroy the reading mechanism and platters.
For quickly destroying hard drives, drive big nails through the entire case in several places. Restoration is at least very manual and annoying, in many cases not worth the effort.<p>If you need more security, building a simple furnace isn't too hard:<p><a href="http://eecue.com/c/driveslag" rel="nofollow">http://eecue.com/c/driveslag</a>
Best method is to use LUKs and then wipe the master key. Luks has a forensic stretching technique to take a 32 byte master key and stretch it to 1 MiB, such that loss of a single bit means the original key is unrecoverable.<p>That really helps you wipe things like SSDs which can copy and migrate data, and make it hard to be certain you destroyed a sector
A friend uses a saws-all (or something of that ilk) and cuts them in half. I'm figuring on taking my old drives to him for that treatment. I don't want to resell them and have a casual snooper recover my data, and I'm not of enough interest for anyone to piece the halves together.
A ferromagnetic cage such as a hard drive enclosure can shield against magnetic fields pretty well. The field lines are concentrated in the enclosure and mostly avoid the inside. I would imagine you need to open the drive up to have much effect.
I normally unsubscribe from junk mail and advertising from e-commerce sites, KJ Magnetics is one of the few exceptions. I always look forward to their emails and blog entries.
take it apart, screw the platters to railroad ties. use belt sander on platter. flip the platters over. repeat. burn sandpaper.<p>take a hammer to platters to seriously deform them and throw them in the trash.<p>not recoverable, imo.
HDD's are shielded with mu-metal: <a href="https://en.wikipedia.org/wiki/Mu-metal" rel="nofollow">https://en.wikipedia.org/wiki/Mu-metal</a>