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It is possible to corrupt data and even destroy a hard drive when running a powerful magnet over it. So I have a few question. Now if the magnet was powerful enough, can a drive be destroyed only if it is on and running or can it be destroyed while it is off/not in use. What about for data being corrupted: does the drive have to be in use or does it matter?

  • This seems obvious and I’m sure the internet abounds with detailed info about this, so for what purpose are you asking? Hard drives store data using minute magnetic fields. Don’t stick a magnet next to them. “How powerful?” - not answerable. – Appleoddity Jun 24 '18 at 6:06
  • Well I am asking for specifics. Not generalizations. – StrangeRanger Jun 24 '18 at 6:07
  • Magnets can destroy hard drives. That answers all your questions, except how big of a magnet do you need. But how can we possibly tell you how strong a generic magnet on Amazon is, where exactly you will stick it, and exactly how much magnetism is needed to affect that exact drive from a manufacturer who probably doesn’t post any data like that? – Appleoddity Jun 24 '18 at 6:11
  • Some reading over here......superuser.com/questions/113430/… – Moab Jun 24 '18 at 12:19
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The data is encoded with tiny magnetic fields on platters inside the hard drive.

It doesn’t matter if the drive is on or off. A strong enough magnetic field will destroy the data on the platters.

Low level information is written by the manufacturer on to the same platters and is not touchable by the OS or user. If that information is also destroyed the drive will be unusable.

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Appleoddity's answer is correct as far as it goes.

But it is extremely unlikely that you'll damage data on a hard drive, let alone damage the hard drive, with anything you'll do with a magnet on the outside of the drive. Affecting the domains on the hard drive requires an extremely high field gradient. In the hard drive this is achieved by having the gaps in the hard drive's heads extremely close to the surface.

In modern hard drives "extremely close" is less than five nanometers - less than a quarter of a millionth of an inch. For comparison, visible light has wavelengths from about 400 to 700 nm.

Consider that there are very strong rare earth magnets inside the hard drive, and they're a lot closer to the platter than you can get from the outside.

See my answer to this related question: Is CRT degaussing really dangerous for nearby laptops?

  • Thank you. I really appreciate your answer and the link to one of you answers that are related to this question. – StrangeRanger Jun 24 '18 at 9:10
  • @StrangeRanger Thank you for the feedback! – Jamie Hanrahan Jun 24 '18 at 18:38
  • I usually don't like the "magnets inside the drive" argument, since the actuator magnets' fields are both carefully oriented vertically and shielded away from the platters. That said, in experiments I've seen with modern drives, you generally need a magnet powerful enough to cause physical head crashes before you can start affecting data directly with the field. – Bob Aug 6 '18 at 6:37

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