Hard Disk Magnet

[bobcat2000]

I met an IT guy who had an electromagnet that looked like a clothes iron.  It was big and heavy.  I asked him what was that for.  He said he used it to wrack the old hard disks before taking them to be recycled.

On the other hand, the recycle place I go to does not use magnet.  They punch a bunch of holes on the hard disks instead.  (And they charge extra $ for that!!!)

This is what I don't get it.

I took apart a hard disk before.  There was a very strong neodymium magnet inside.  Wouldn't that magnet damage the disks next to it?  or the entire thing about using magnetic field to wipe the data off the hard disk is just a myth?

[Circlotron]

For the magnet inside the HDD, the field goes from one magnet, through the actuator coil, then into the facing magnet. Very little field spreads out from this air gap. It is much much happier to go straight to the other magnet. If it did spread out you would certainly have problems.

[AntiProtonBoy]

If the drive is functional, zero formatting does a pretty good job, and chances of data recovery after that is pretty much zero. That said, this approach may not be very practical, if you need to wipe lots of drives.

[bobcat2000]

Destroying the hard disk is not enough.  Any monkey can punch holes to the hard disk and wipe it with zero.  The law requires the "process" to be certified.  (i.e.) This monkey needs to take the hard disk to another monkey that is licensed by the board.  Only the licensed monkey may punch holes to the hard disk.

[ejeffrey]

I met an IT guy who had an electromagnet that looked like a clothes iron.  It was big and heavy.  I asked him what was that for.  He said he used it to wrack the old hard disks before taking them to be recycled.

On the other hand, the recycle place I go to does not use magnet.  They punch a bunch of holes on the hard disks instead.  (And they charge extra $ for that!!!)

This is what I don't get it.

I took apart a hard disk before.  There was a very strong neodymium magnet inside.  Wouldn't that magnet damage the disks next to it?  or the entire thing about using magnetic field to wipe the data off the hard disk is just a myth?

It's very unlikely that the IT guy's magnet can erase a hard drive.  It just puts on a good show. The field falls of pretty quickly away from such a hand-held magnet or degausser, and it actually takes a fairly strong field to do so.  This is also why the Nd magnets in the drive motor don't really affect the media.  Nd magnets can erase softer magnetic storage like credit cards if placed right against them but the magnets in the drive motor mostly have their field concentrated inside the motor.  It's possible that it can damage the head assembly or electronics of the drive rendering it inoperable without affecting the magnetic media itself.

And now you have understand why in security conscious places they require a certified person to do data destruction: random IT guys might think their impressive looking magnet is doing the job.

[wraper]

Erasing HDD with electromagnet is real. There are even emergency degaussers mounted inside a computer with remote kill switch. FBI open up! Press the switch, data gone.

[wraper]

This is also why the Nd magnets in the drive motor don't really affect the media.  Nd magnets can erase softer magnetic storage like credit cards if placed right against them but the magnets in the drive motor mostly have their field concentrated inside the motor.  It's possible that it can damage the head assembly or electronics of the drive rendering it inoperable without affecting the magnetic media itself.

Those Nd magnets inside HDD are shielded with barely any magnetic field leaking outside.

[bobcat2000]

It's very unlikely that the IT guy's magnet can erase a hard drive.  It just puts on a good show.

He knows what is doing.  He just doesn't trust those guys in the e-waste place.  And that magnet iron is huge.  It will melt T-X in no time.

[CJay]

HDD manufacturers made it pretty easy a few years ago, one good throw onto a concrete floor and bang, the data is gone because a lot of drives used glass platters.

Have worked in places where drives are shredded in house so there's no chance of external contractors making a 'mistake'.

[Gregg]

For my personal hard drives, I prefer the target practice method of obliterating the ability to recover data...   It is quite satisfying.

[StillTrying]

The disks in this one I opened weren't glass, they were very tough. I lost many 1000s of photos on it.
The groove near the hub vanished the head completely leaving a very fine black dust everywhere.

[nightfire]

Of my experiences researching stuff before as I was tasked to design the process of getting rid of old HDDs at my last employer (datacenter):

- Todays HDDs mostly use PRML recording
- The magnetic field their own heads are able to generate are several magnitudes stronger than what most external magnets can do, unless they are pulsed


Therefore for wiping a disk clean, I had some talk with a data recovery lab and they also told me, that after a wiping where every sector has been touched (bit flipped) they won't be able to recover that. I asked to that getting in written, and the sentence addendum "in civilian data recovery" irrritated me a little bit ;-)

So: As long as a HDD will work, use a software that does 3 tries to overwrite every sector with bit complements. ASCII "0" is not digital null...
The DoD Short algorithm usually is more than sufficient for that.
But beware: A HDD usually has reserve/spare sectors, that get exchanged for bad sectors- if the wiping software cannot get to them (maybe because running from some plain operating system with standard drivers) this area will not be handled.

Other solution: Degauss it with special equipment, basically you generate some electromagnetic shock that will destroy every information on the platter, including the factory-written servo track- but at the factory a HDD can be low-levelled and would be good for re-use as refurbished part...

[bobcat2000]

Ok.  So, Magneto can throw my hard disks all day long.  He will not get rid of my pictures with Mystique.

[nightfire]

Well, depending on the duration and power of said magnete, I would not like to put my hands above burning wood or similar stuff...
It should not, but it could over time cause some other nasty stuff that will degrade performance.

And if someone says Gutman: This algorithm collection has been thrown together to use mechanisms suited for mostly vintage media like floppy disks and due to the variety of physical media, to have at least some appropriate algorithm that would actually wipe data- using that 35pass stuff on modern media is wasted time.

[DiTBho]

Destroying the hard disk is not enough.  Any monkey can punch holes to the hard disk and wipe it with zero.  The law requires the "process" to be certified.  (i.e.) This monkey needs to take the hard disk to another monkey that is licensed by the board.  Only the licensed monkey may punch holes to the hard disk.

( Emmm ...  I was one of those "monkey" in 2005, it paid my university  )

[DiTBho]

So: As long as a HDD will work, use a software that does 3 tries to overwrite every sector with bit complements. ASCII "0" is not digital null...

Special pattern in Badblocks does { 0xff, 0x55, 0xaa, 0x00 }

[ejeffrey]

Erasing HDD with electromagnet is real. There are even emergency degaussers mounted inside a computer with remote kill switch. FBI open up! Press the switch, data gone.

It's certainly possible, but you need a really strong field, typically 1-2 tesla at the platter.  HAMR will require even more than conventional drive materials.  Even if you achieve this field strength at the surface of your magnet the field will fall off pretty quickly, guaranteeing that you have a strong enough over the platters is quite difficult, especially with a hand-held magnet.  Data destruction degaussers keep high field strength by putting the whole drive inside the solenoid.

An "emergency" degausser mounded inside a computer case is honestly a stupid movie trope.  Not that it is impossible or hasn't been done in real life, but it is an unnecessarily expensive and complicated way to achieve the goal.  Data destruction degaussers are designed for high throughput destruction of hard drives that have been removed from service especially when you don't know their history.  If you are doing something where you think setting up a system like that is a good idea you would be much better off using full disk encryption and just erasing they key as the self destruct.  That is faster, cheaper, more reliable, and requires less standby power to accomplish the same goal.  It is just less flashy.

[wraper]

you would be much better off using full disk encryption and just erasing they key as the self destruct

If there is a key, then someone who knows the key can be persuaded to reveal it or erasure of the key might not work as well as you may think. Also as of hardware encryption and TPM, time has proven they often have some bug or backdoor which can allow decryption. Even if they don't, they can be cracked given enough resources are thrown at the problem. Like by digging into a chip with ion beam and probing it's internals.

[wraper]

If it was me, I probably would use encryption and store data on SSD with high current voltage source attached to NAND VDD so it can be reliably overvolted when needed.

[Raj]

Never seen a hard drive survive a drop from 4 story building.(shattered platter)
Failing which, a screwdriver can help open it and get the job done
Who would want to pay someone to destroy them?
But there's a video on YouTube with a guy, with magnet as huge as the drive itself, erasing drives with it.

[Kleinstein]

Modern HDs usually have a pretty soft case - often just a metal coated foil. So mechanically punching through and shattering the platterns should be relatively easy.

The Fields to reliably erase the data are quite strong and hard to get from a permanent magnet. The case (especially cast aliminum) can shield against fast puslsed fields.
There is still a good chance to damage some data, so to the OS the disc may look bad, but much of the data may still be there.