
The Helium Factor and Hard Drive Failure Rates - ingve
https://www.backblaze.com/blog/helium-filled-hard-drive-failure-rates/
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jarvist
You'd certainly expect the long-term failure for Helium filled to be lower. By
displacing (moist) air, you've completely stopped any metal corrosion. Helium
is also highly conductive to heat, so you will even out any hot spots.

Does anyone know to what sort of pressure helium the drives are filled?

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tedunangst
Is the thermal conductivity of helium actually relevant to hard drives? Like
what kind of hot spots and transfer rates are we talking about?

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HankB99
FWIW utility generators are cooled with hydrogen to reduce windage losses and
promote cooling. Hydrogen is probably lower viscosity and higher thermal
conductivity than helium. It's also very hard to contain due to the small
molecular size and has the widest flammability range of any gas with which I'm
familiar, making it an interesting gas to work with. ;)

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frandroid
The utility generators probably don't worry too much about leaks, since they
can just refill with new, abundant hydrogen, too.

It would be amusing to have a hydrogen-cooled hard drive for which you'd have
to regularly refill the water tank so that it could generate more hydrogen for
itself. :)

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tzahola
Yeah, and it would have a little Bunsen burner to safely get rid of waste
hydrogen!

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HankB99
Yes, it's the hydrogen that leaks out that's the problem. I was told that the
way to find hydrogen leaks in plant piping was to walk the line holding a corn
broom over the line. When it bursts into flame you found the leak. In an
enclosed space it can form an explosive mix with air if it doesn't ignite
before it accumulates.

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mrtnmcc
If you model drive failure as a Poisson Process (each drive flips a coin each
day with probability of failure x), then the measurements imply air and helium
drives both have about x=2.8e-5. But drive failure rate may not be constant
over time, especially if the failure is wear/aging related. The author should
consider fitting the data to a
[https://en.m.wikipedia.org/wiki/Weibull_distribution](https://en.m.wikipedia.org/wiki/Weibull_distribution)
with k>1.

In particular, k=2 is a model where failure rate increases linearly over time.
To estimate the instrinsic drive failure rate for this model, we must look at
the raw failure times (not enough info in blog's totals table) and compute the
root-mean-square of time between failures. Then divide this by the total
number of drives. Do this for the two classes (air vs helium) and see which is
better.

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titzer
> If you model drive failure as a Poisson Process (each drive flips a coin
> each day with probability of failure x)

IIRC the Poisson distribution applies when the rate is roughly constant per
interval of time, which is not exactly the same as a probability of x per
interval of time. (Failures are independent in the latter, not in the former).

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mrtnmcc
Please see Poisson Process, which is different than Poisson distribution,
[http://www.randomservices.org/random/poisson/index.html](http://www.randomservices.org/random/poisson/index.html)
.. failures are indeed independent.

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outworlder
Given the amount of engineering required for drives which are able to contain
helium, one would expect that the required tolerances and materials would be
much better. There may be reliability advantages for Helium, but I suspect
greater care and QA during manufacturing will account for most of the
improvement.

Also, it would be very bad PR for a new type of drive if they performed
significantly worse.

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tlb
I might have expected the first-order effect to be that helium drives run
cooler, and therefore last longer. Most failure mode rates have an eᵏᵀ term,
doubling every 10-15 °C. But Google's large study didn't show much of that at
reasonable temperatures (below 45 °C):
[https://static.googleusercontent.com/media/research.google.c...](https://static.googleusercontent.com/media/research.google.com/en//archive/disk_failures.pdf)

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ChuckMcM
I absolutely expect helium drives to run cooler simply because helium is a
much better conductor of heat compared to air. As a result all heat generated
in the drive cavity will be more effectively conducted to the containment
vessel and leave the material inside consistently cooler.

~~~
jacquesm
That's a two way street though. If the ambient is higher it will carry the
heat from the outside into places in the drive where it can do real damage.

~~~
ChuckMcM
For an excessively hot exterior sure, but I was thinking back to an experience
at NetApp when thermal inside was the issue. When NetApp first started using
SATA drives (rather than Fiber Channel) in their Nearstore appliance we
discovered that the SATA drives were negatively effected by writing too much.
Specifically, if write duty cycle was too high, the r/w head got too hot, and
the heat caused it to change shape slightly and that shape change caused it to
fly higher. Leading to something that was dubbed 'high fly writes' which
splattered into adjacent tracks and could corrupt data. One fix was to keep
track of the write duty cycle and to let the drive 'rest' for a bit to keep
the overall duty cycle into something the drive could handle.

I don't think that sort of failure can happen on a helium drive.

~~~
jacquesm
You're right about that, in a drive filled with helium inside the drive the
temperature gradients will be flatter.

Heat transfer in computing hardware is a super interesting subject.

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djsumdog
Pretty interesting. I like how the author talks about how it may be too early
to get useful data yet since their non-helium drives have been online for much
longer.

It'd be interesting to look at the numbers again in two years and see if the
guess is correct.

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atYevP
Yev from Backblaze here -> we're going to keep an eye on them and follow up on
the stats so that we can eventually get there!

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tux3
If the AFR numbers follow some bathtub-shaped curve, would it make sense to
use that curve to "normalize" the failure rates according to drive days?

I always wonder if the rates we see for each drives are really comparable,
since they all have different ages, and whether that's representative of the
average lifetime AFR.

That might be an interesting column to add to the reports!

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atYevP
This might be interesting -> [https://hackernoon.com/applying-medical-
statistics-to-the-ba...](https://hackernoon.com/applying-medical-statistics-
to-the-backblaze-hard-drive-stats-36227cfd5372) it's more "time based" \- a
medical statistical model applied to our drive stats!

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b11484
In the article it states that the helium can typically reduce drag by 20%. How
much of an effect does that have on the cost of powering the drive? I assume
it would at least be less than a 20% improvement overall.

~~~
atYevP
Yev from Backblaze here -> You'd have to look at the entire cabinet to get a
better sense of the power savings. Post author Andy explains a bit more here
-> [http://disq.us/p/1s8psup](http://disq.us/p/1s8psup).

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ThePhysicist
Maybe this is a stupid question, but why don't manufacturers evacuate the
drives (i.e. create a vacuum) instead of filling them with Helium?

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jarvist
It's much easier physically to build something which can hold e.g. +0.1
atmosphere helium, than resist imploding against -1.0 atmosphere. Practically
speaking, pumping down to vacuum is a slow process, whereas you can flush with
an inert gas. Finally, hard-drive heads actually float on lamina of gas; this
is one of the reasons that normal open-circuit hard drives have a maximum
operating altitude.

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rconti
Wait, if it's +0.1 atm helium (for example), what happens if it develops a
slight leak, a leak from which helium molecules can escape but air molecules
cannot? once the pressure reaches equilibrium, there would be no reason for
additional helium to escape, and because air can't enter.... then what?

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rleigh
That isn't how it works though--look up partial pressures of gases. Helium
will continue to escape until its partial pressure is at equilibrium with the
external environment, i.e. near to zero, and the external gases will enter
until they are at equilibrium with the internal environment. At that point the
partial pressure of each gas will be equal on both sides.

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ak217
What happens to these helium hard drives if you repeatedly cycle the pressure,
like by taking the hard drive on an airplane?

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rleigh
Since the partial pressure of helium at ground level and flight level is
essentially the same (≈0) there should be very little change, providing the
seals are intact. Since they are very securely sealed to contain the helium,
changes to the external pressure, unless extreme, should not have any
significant effect.

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11chris11
have there been any drives designed with an array of fixed read / write heads
i.e. one per track or a head that can access multiple tracks on a platter
simultaniously?

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krallja
There have been a few. Here’s an older article
[https://www.tomshardware.com/news/seagate-hdd-
harddrive,8279...](https://www.tomshardware.com/news/seagate-hdd-
harddrive,8279.html)

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jammi
Just like in combustion engines, it seems like the best things are held to the
last generations of hardware. I expect both to lose market share down to nil
during the 2020s. BEVs replacing internal combustion engines and solid state
storage replacing HDDs even in cost per storage unit.

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ableal
"Perfection is attained on the point of collapse"

(I thought I had read that somewhere, but the closest I find now is C.N.
Parkinson's formulation, which I did read years ago ...)

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the_cat_kittles
ever tried pulling a vacuum on a normal drive? does that work?

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blackflame7000
Air is required for the heads to function. While the disk's internal
environment is separate from the outside air to keep it clean, air exchange is
permitted between the outside and inside of the drive to allow the drive to
adjust to changes in air pressure caused by thermal expansion. A special
"breather" filter is installed to prevent foreign matter from contaminating
the drive.

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lowestprimate
Helium also has higher viscosity than air and because of that the flying head
in the drive is more stable than in air.

