Yeah, I hope people realise that everybody has these magnets IN their computer. You might have a NAS in which case you have several of these magnets much closer than 6 inches to the other drives and power supply and nothing happens.
Magnets near your or even on the computer do nothing.
Yes. The magnet is stationary and the spinning drive plate is moving the data, the conductor, very rapidly relative to the magnet. (imho the real issue is the large metal box surrounding the drive plates. It's hard to feel a magnet from inside a metal house.)
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.
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 have a coil of wire, too.
If HDD magnets overwriting nearby HDD data was a thing, it would be happening all the time.
If HDD magnets in motion in certain orientations were inducing damaging currents in nearby HDDs or in nearby power supplies which then damaged connected components, that would be happening less often but still all the time. Not all chassis designs have power supplies at the opposite end as the disks, and some applications like consumer NAS boxes have them in close proximity to each other.
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.
Magnets near your or even on the computer do nothing.