SMART-supporting HDDs can execute several kinds of self-tests, e.g. long test, short test or conveyance test.
On Linux these can executed with "smartctl", which can also be used to read the error logs after the tests finish. The long test can take almost a day on big HDDs, while the other tests take only a few minutes.
After I had some problems with a bad HDD, I have begun to always execute all the SMART tests whenever I buy a HDD. Of course, if any test fails, the HDD must be returned immediately and the vendor cannot refuse to replace it when the request is backed by the failed SMART acceptance tests.
This is a good habit, because even if such events are very rare, I have still encountered a few HDDs that have failed the tests, so I have returned them and I have received other good HDDs.
How do you generally know when the long test is over? Is there a way to get a notification of completion? Is it ok to begin using the drives while testing? I personally run my new drives through a few rounds of badblocks
What would happen if you had a rigid structure that helium could permeate, but nothing larger could, and then filled it up with helium and waited?
Would most of the helium exit, until it was balanced with just the partial pressure of helium in the atmosphere? That would be nearly a vacuum, wouldn't it?
> Pretty sure it would simply equalize to the external pressure.
External partial pressure of helium which is extremely low.
> Consider it another way. If you have such a device with a vacuum inside, would it not pull in the external helium over time to reduce the vacuum?
It would, but only until the partial pressure of helium inside is equal to the partial pressure of helium outside (assuming the membrane is permeable only to helium). After that point the same amount of helium will traverse both ways, establishing the equilibrium.
Internal pressure would equilibrate to the partial pressure of helium in the atmosphere, presuming all other species can be assumed to have zero permeability. Osmotic pressure/semipermeable membranes is the analogous liquid system.
It would be a vacuum I guess, but generally not in the normal sense because this is the case with most metals. You don't really consider the interstitial space between the atoms in the crystal lattice a vacuum even though there is space for small atoms (He/H) to diffuse through.
Ignoring the fact that what you're describing sounds suspiciously like a Maxwell's demon, I think the equilibrium would be at a higher pressure because helium escaping against an overall pressure gradient would be doing work.
In essence, at the boundary I think the rate at which helium escapes would not simply be proportional to the gradient created by the internal pressure and the exterior partial pressure, but I think would include a term involving the whole exterior pressure.
It's not a Maxwell daemon, it's just a device for which nothing but helium exists. In the ideal gas model it would indeed create almost vacuum but the second law of thermodynamics is not violated since the process is symmetrical. Pressure of helium outside is also almost zero.
This relates to the difference between how a real gas and how an ideal gas behave in this scenario.
The difference in this situation will be very small in my opinion, broadly because the gas molecules in the atmosphere still have comparatively high mean free paths and therefore won’t interact with the “escaping” helium molecules.
I don't know the answer, but this does make me think of atomic sieves like the ones used in oxygen concentrators.
This is an armchair scientist explanation of them, but they "concentrate" oxygen by first having atmospheric air pumped in and then pressurized. The microsieves have holes so small that mostly only oxygen can fit through, the larger CO2 and Nitrogen atoms simply won't fit.
Then, pressure is let off and fresh air brought in. The fresh air scrubs out the oxygen depleted air and refreshes it with standard air.
Then, the pressure decrease allows the oxygen to leak back out of the sieves, leaving you with oxygen enriched air.
I don't know if there are any atomic helium sieves, but if you can find one it might be a start to testing the question.
It would create an almost perfect vacuum. You could then extract work by collapsing the vessel. The free energy for the work would come from putting the trapped helium (state 1) in a higher entropy state (state 2).
For what it's worth, this is done industrially to separate gasses using porous membranes.
Fun fact: the Rolex "deep sea" sea-dweller contains Helium and an Helium valve. I'm not too sure how they keep the Helium from escaping. James Cameron (who made the movie The Titanic) actually strapped a Rolex sea-dweller "deep sea" to a little robot submarine and sent it to 10 000 meters deep to see if Rolex was full of shit or not.
Turns out the "veblen good" did quite well and didn't break.
And James Cameron got a limited edition Rolex Sea-Dweller deep sea model named after him.
You have this backwards, the valve is to let the Helium out.
The watch was designed for saturation diving - people essentially living at high pressure in a pressure cylinder, breathing a mixed gas which includes a high helium percentage (as nitrogen becomes narcotic). This saved them hours of decompression every dive - just do one decompression at the end of the job.
The problem was despite all of the seals to withstand seawater, the watches would let helium in & gradually equalise the internal & external pressures. All fine until they came up to the surface, when the watch would blow the crystal off, as the helium couldn't escape quickly enough to equalise. The Helium valve is there to release this pressure on ascent.
The sea dweller was designed as a highly specialised tool for a specialised industry, before becoming luxury item.
Here’s a diver checking out an air pocket in a sunken boat finding someone alive in an air pocket (most of the recording is the guy at sea level, but you really get the chipmunk from the diver):
Note that it's possible to (mostly) hermetically-seal non-helium, air-exchanging breather holes of HDDs for use in submerged mineral oil applications. It's typically done by adhering a flexible membrane over the air port.
Are HDD's a significant consumer of the world's helium, in the scheme of things? I had thought helium was used only in a few bleeding edge drives, and they went to normal air as the tech matured.
Helium drives are basically standard for enterprise hard drives now. The reduced drag force allows for using thinner drive platters (helium drives can hold up to 10 platters, while air-filled drives can only hold up to 6 platters) which boosts capacity. Helium drives also use less power, run cooler, and the helium gas helps to absorb vibrations that can cause wear and tear (useful in enterprise settings where you have 45 or more drives in a 4U chassis).
Yep, it says right there that a "standard" helium tank is adequate to fill 10,000 hard drives. I am going to assume that by "standard" they mean 220ft^3 or 250ft^3, even though my "standard" for tanks is 125ft^3 because I can comfortably carry one of those on my shoulder.
Helium in the atmosphere is almost two orders of magnitude more common than xenon and three times as concentrated than krypton. Both are extracted from air.
Even though He is constantly venting to space, alpha emitters keep replenishing it.
Cheap helium from 7% CH4 wells is not going to last. But we're not going to run out of He. Just the energy to extract it.
Assuming a drive contains helium at standard temparature and pressure, and contains about a liter in volume. That would be about 1 gram worth of helium per drive.
0.05 gram Helium assuming: (1) half of drive volume is used for platters, (2) at 15° Celcius (3) at 1 atmosphere (I'm guessing not pressurised since that would defeat purpose of using Helium, although might be less than 1 atmosphere)..
0.376 litres for total 3.5-inch HDD volume from my first Google result: "Width: 101.6 mm, Height: 25.4 mm, Length: 146 mm". Actual volume used for platters is less than that.
Helium is light ~ 0.169 g/litre from "0.169 kg of Helium is 0.999 m3 at 15°C": https://microsites.airproducts.com/gasfacts/helium.html Note that I think comment assumed one litre of normal air not Helium: "The density of dry air is 1.2929 g/litre at STP".
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).
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.
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.
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%.
Readit News
It's an immediate "return the drive" scenario, as something happened between factory and the SMART test and the drive is no longer within spec.
Thankfully an easy returns and replacement process, but an eye opener too, I hadn't heard of SMART 22 prior to this.
On Linux these can executed with "smartctl", which can also be used to read the error logs after the tests finish. The long test can take almost a day on big HDDs, while the other tests take only a few minutes.
After I had some problems with a bad HDD, I have begun to always execute all the SMART tests whenever I buy a HDD. Of course, if any test fails, the HDD must be returned immediately and the vendor cannot refuse to replace it when the request is backed by the failed SMART acceptance tests.
This is a good habit, because even if such events are very rare, I have still encountered a few HDDs that have failed the tests, so I have returned them and I have received other good HDDs.
Would most of the helium exit, until it was balanced with just the partial pressure of helium in the atmosphere? That would be nearly a vacuum, wouldn't it?
Consider it another way. If you have such a device with a vacuum inside, would it not pull in the external helium over time to reduce the vacuum?
External partial pressure of helium which is extremely low.
> Consider it another way. If you have such a device with a vacuum inside, would it not pull in the external helium over time to reduce the vacuum?
It would, but only until the partial pressure of helium inside is equal to the partial pressure of helium outside (assuming the membrane is permeable only to helium). After that point the same amount of helium will traverse both ways, establishing the equilibrium.
Since this hollow core would be much larger than the crystalline structures in a metal would this not therefore be a very weak comparison?
Ignoring the fact that what you're describing sounds suspiciously like a Maxwell's demon, I think the equilibrium would be at a higher pressure because helium escaping against an overall pressure gradient would be doing work.
In essence, at the boundary I think the rate at which helium escapes would not simply be proportional to the gradient created by the internal pressure and the exterior partial pressure, but I think would include a term involving the whole exterior pressure.
The difference in this situation will be very small in my opinion, broadly because the gas molecules in the atmosphere still have comparatively high mean free paths and therefore won’t interact with the “escaping” helium molecules.
I don't know the answer, but this does make me think of atomic sieves like the ones used in oxygen concentrators.
This is an armchair scientist explanation of them, but they "concentrate" oxygen by first having atmospheric air pumped in and then pressurized. The microsieves have holes so small that mostly only oxygen can fit through, the larger CO2 and Nitrogen atoms simply won't fit.
Then, pressure is let off and fresh air brought in. The fresh air scrubs out the oxygen depleted air and refreshes it with standard air.
Then, the pressure decrease allows the oxygen to leak back out of the sieves, leaving you with oxygen enriched air.
I don't know if there are any atomic helium sieves, but if you can find one it might be a start to testing the question.
For what it's worth, this is done industrially to separate gasses using porous membranes.
Turns out the "veblen good" did quite well and didn't break.
And James Cameron got a limited edition Rolex Sea-Dweller deep sea model named after him.
The watch was designed for saturation diving - people essentially living at high pressure in a pressure cylinder, breathing a mixed gas which includes a high helium percentage (as nitrogen becomes narcotic). This saved them hours of decompression every dive - just do one decompression at the end of the job.
The problem was despite all of the seals to withstand seawater, the watches would let helium in & gradually equalise the internal & external pressures. All fine until they came up to the surface, when the watch would blow the crystal off, as the helium couldn't escape quickly enough to equalise. The Helium valve is there to release this pressure on ascent.
The sea dweller was designed as a highly specialised tool for a specialised industry, before becoming luxury item.
https://www.youtube.com/watch?v=wusrtGfjzZg
https://youtu.be/LrvRwNaE7Eo?si=bmFzXBmiC1QUwnIF
edit: the close up in the Wikipedia article actually is from a hard drive
Yep, it says right there that a "standard" helium tank is adequate to fill 10,000 hard drives. I am going to assume that by "standard" they mean 220ft^3 or 250ft^3, even though my "standard" for tanks is 125ft^3 because I can comfortably carry one of those on my shoulder.
Even though He is constantly venting to space, alpha emitters keep replenishing it.
Cheap helium from 7% CH4 wells is not going to last. But we're not going to run out of He. Just the energy to extract it.
0.376 litres for total 3.5-inch HDD volume from my first Google result: "Width: 101.6 mm, Height: 25.4 mm, Length: 146 mm". Actual volume used for platters is less than that.
Helium is light ~ 0.169 g/litre from "0.169 kg of Helium is 0.999 m3 at 15°C": https://microsites.airproducts.com/gasfacts/helium.html Note that I think comment assumed one litre of normal air not Helium: "The density of dry air is 1.2929 g/litre at STP".
But their website looks pretty stale, and I don’t see evidence of traction from brief Googling.
https://en.m.wikipedia.org/wiki/Cold_welding
Deleted Comment
Why?
It's used in power station generators. Why would a hard disk be interesting?
https://en.wikipedia.org/wiki/Hydrogen-cooled_turbo_generato...
Deleted Comment
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%.
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 :)