Jim wrote:
On 05/01/2019 08:33, Paul wrote:
Even hard drives soon, by design, won't have "longevity". The
industry seems to be headed towards an "all-Helium" future.
My favorite air-breather is discontinued, and I seem to be
seeing a stack of Helium drives with linear pricing. The
Helium is guaranteed to stay inside the drive for (5) years.
If I wanted to dig a hole in the back yard, drop a Helium drive
in the hole, what would I find 20 years from now ? Whereas
with an air-breather drive, you'd still have something.


Paul

Paul can you explain this a wee bit more for me or point me in the
direction of some reading regarding "all-Helium & air-breather"? Most of
my spinners are WD Blacks and Greens and about 70% being Blacks

Ordinary disk drives do not have a vacuum inside.

They're filled with air.

There's a hole in the HDA, that lets air in and out.
Underneath the hole is a disc made of fibers and it's
a hepafilter. It keeps dust from getting inside the drive.
Even though air is freely exchanged through the hole (slowly),
the inside of the drive is still "Class 10" on cleanliness.

The ordinary hard drives actually have more than one hole.
There's a hole for the servowriter arm to be shoved inside
the drive and write a servo pattern. After the pattern is
written, the arm is withdrawn and a sticker covers the hole.
You might not have noticed because of the color they
selected for the stickers, but they're relatively
flimsy compared to the milled box used for the base
of the drive.

The stickers could not afford to be pressurized, so instead
the drive is allowed to equalize pressure. The drive is rated
to work, up to 10,000 feet or so. (The heads won't "fly"
quite as well in Denver.)

*******

The new drives are sealed. No more servowriters. No more
stickers. You might even see a lack of screws. The drive
is filled with Helium gas. Air filled drives hold four platters.
Helium drives can have seven+ platters. (They're even making
thinner platters for those drives.)

Helium is less viscous. The motor doesn't have to work
as hard to spin the platters with only Helium to provide
"air friction". And Helium is a slightly better conductor
of heat, so the HDA gets the heat a bit easier. That might
make a difference to the microscopic conditions around
the head assembly while it's flying or something.

On the one hand, the drive is in less danger of getting
dust inside. With no breather hole, there's no easy way
for the breather to be compromised (when your house floods
and your desktop computer is flooded with water). The
Helium drive has that covered, except dirty flood water
can still short out sensitive circuits on the
controller board. But at least you don't have to
worry about the HDA "flooding".

Will there still be Helium in the Helium drive ten
years from now ? We don't know for sure. Accelerated
life testing tries to answer that question, but then
it's a question of whether the test case is "representative"
or not of real conditions and how the materials will "age".

The secret to sealing the Helium in, isn't the welded cover.
There is a separate cover with a wide adhesive edge finish.
The adhesive is deep enough from the outside of the
cover inwards, that the Helium "has trouble escaping".
It's the depth of the adhesive that keeps the gas in.

I presume any welded covers you find, are for mechanical
protection. A weld would likely leak, as it would be
difficult to make a liquid metal seam that was gas tight
after it cooled off. Such a metal cover can be "transparent"
to a gas like Hydrogen, but Helium is big enough that
it's possible to hold it with regular materials. I think
metals leak Hydrogen around 500C or so (goes through
pretty easily then). Helium is still a bitch, but
not nearly as bad as some of the properties of
Hydrogen. (Exploding is just one of the properties
that matter for Hydrogen :-/ ) The adhesive holds
the He gas, but other solutions "help keep the cover on".

You can't very well put screws through the cover,
because the adhesive would have to make a wide
swath around each screw.

Like everything disk drive companies do, it's pretty crazy
stuff. But the change in the product lineup last year,
suggests they'll give up on air breathing drives entirely.
If they'd kept my favorite drive around, I would have
continued to believe the low capacity drives would use air,
and only the more expensive high capacity ones would use
Helium.

With the air-filled drives, there's nothing to escape, so
20 years from now it's just a matter of whether the motor
still has lube in the spindle bearing. Everything else in
the drive should hold up well. As long as the two drops
of oil stay in the FDB motor, it's frictionless.

Paul