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Comment by wigster | Hacker News Reader

if helium is better, why not use a vacuum?

A gas provides a "bearing" for the heads to ride on as the disk spins below it.

Right you are, forgot about that completely! IIRC this is important to prevent a headcrash if the drive is jolted while in operation (of course within certain limits).

It's required to work at all, not just as some kind of guard rail. It's like the oil in a normal bearing, the oil isn't just to prevent a crankshaft crash in case the car is jolted while in operation, the oil is a part of the way the thing functions at all in the first place.

Maybe magnetism could work. HDD platters take very strong fields to change magnetization these days, so erasing the data with the positioning magnet(s) seems avoidable.

So write too many zeros to your drive, the disk becomes demagnetized, and the head will crash?

With another encoding like Manchester, it wouldn't;-)

The raw words written to the drive are actually re-encoded into slightly larger codewords with nice properties like not having too many zero or one bits in a row, and error detection/correction.

Plus I think that the 0/1 bits are not encoded as "no magnetism"/"some magnetism", but instead as "north magnetism"/"south magnetism" since magnetic fields have a direction.

And I don't think the magnetic fields on the platters have any appreciable effect on the head besides the electromagnetic effects at the sensor.

Essentially the same problem as with fiber optics. The data can't be recovered unless there are frequent bit transitions. In that case the data is transformed to ensure illegal patterns cannot occur.

Also, you could imagine a magnetic bearing whose field strength rapidly diminishes as you move away from it, due to cancellation, like a Halbach array [0]. I wonder if there's a simple geometric configuration for a bearing that has this property, as well as the critical property of passively stable levitation, maybe based on diamagnetic or superconducting materials [1].

edit: Maybe something in this direction? [2]

[0] https://en.wikipedia.org/wiki/Halbach_array

[1] https://en.wikipedia.org/wiki/Magnetic_bearing

[2] https://ntrs.nasa.gov/api/citations/20070006849/downloads/20... ("Development and Testing of a Radial Halbach Magnetic Bearing")

A startup called L2 drive is apparently working on this: https://l2drive.com/vacuum-hdds-the-next-logical-step-after-...

But their website looks pretty stale, and I don’t see evidence of traction from brief Googling.

Heads ride on cushion of gas, would instantly friction weld into platters in vacuum.

Friction or cold/vacuum welding at that point?

Metal sticks to each other in vacuum

https://en.m.wikipedia.org/wiki/Cold_welding

Is heat a concern in HDDs? Vacuum would probably make it extremely difficult to cool if it's necessary.

No friction ... No heat

Sounds like an SSD..

SSDs can get pretty hot though.

SSDs have lots of moving parts and friction, all the electrons are zipping around the circuits with friction. This creates heat :)

Heat can still circulate through the metal parts. Which is a better heat transfer medium than air anyway.

Hydrogen would also be .. interesting ...

Oh, the huge HDD.

Wouldn't be a fire risk because there's no oxygen available. But hydrogen is chemically reactive and over time it could corrode or weaken the materials inside the HDD.

That's not the main problem. The main problem is hydrogen is fucking painful to contain.

Not as painful as helium. Bigger atom but it leaks more.

Ah, truth. Brain fart.

ASME Boiler and Pressure Vessel Section V

Helium leak detection sensitivity is 3 orders of magnitude higher.

Memory is fallible, but the code doesn't lie.

Hydrogen even diffuses through (and into) metal - seems not doable, not cheaply and without maintenance at least.

Helium atoms are actually smaller than hydrogen atoms, and much smaller than hydrogen mollecules.

While that is true, there are metals through which hydrogen can diffuse faster than helium, because the hydrogen molecules dissociate and ionize when entering the metal and the hydrogen ions diffuse through the metal individually.

> Hydrogen would also be .. interesting ...

Why?

It's used in power station generators. Why would a hard disk be interesting?

https://en.wikipedia.org/wiki/Hydrogen-cooled_turbo_generato...

Cause exploding hard drives are metal AF

It won't explode until it's mixed with oxygen.

Hold my beer.

The small amount contained in the HDD would a minimal risk.

Larger amounts handled in the manufacturing process, OTOH...

I'm curious how the shaft seals for generators manage to seal the hydrogen. Perhaps the hydrogen is contained within the the generator and not exposed to the seals, though I thought one of the reasons for its use (along with cooling) was reduced windage losses.

Maybe structural issues in trying to stop the case from imploding?

vacuums tend to collapse on themselves, I think it might be more costly in structural elements to prevent that?

It is better to think of a vacuum within air to be similar to a bubble underwater.

Air is like water in other ways too. We slightly "float" in air by the weight of air we displace. e.g. 80kg person is approximately 80 litres (density of a body is 1.010 kg/litre). Weight of displaced air is approx 0.1 gram (1.2929 gram/litre). So the floating effect of air reduces your weight (not mass) by about 0.1%.

> It is better to think of a vacuum within air to be similar to a bubble underwater.

I don’t think it is vey similar. That bubble pushes against the water to maintain itself; it manages to do that only because its “push” increases the higher its pressure and it is more compressible than water.

The vacuum, on the other hand, is compressible (if you want to call that so), but its “push” remains zero if you do, so it needs help to push against the air to maintain itself.

That’s why the post your replied to said “vacuums tend to collapse on themselves, I think it might be more costly in structural elements to prevent that?”

Thermoses have vacuum in the walls, and they are very thin, much thinner than a hard-drive case.

I think they do get designed specially for resisting the vacuum collapsing the walls, but you're right, it can probably be done!

What about a partial vacuum?

Perhaps there is a hapy medium between air resistance and cushioning? Reducing the air by an amount might help.

Although, I'd be surprised if they hadn't thought of this already :)

a partial vacuum of only helium, tightly sealed to keep in the helium. The tight seals will work to make sure that when there is leakage, only helium leaks in. and if there is no helium component to the air outside, you'll just get helium leaking out thus improving your vacuum.

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