Building any appreciable amount of compute capacity (on the scale of, let's say, a single large datacenter in northern VA) inside a mountain also becomes a huge heat rejection problem, since with the exception of the 0.00000000001% that leaves the facility as photons down a SM fiber cable, 100% of the energy consumed is turned into heat.

So you build your stuff inside a mountain and run a bunch of big ass liquid cooling loops to heat exchangers in the atmosphere outside the mountain. The requirement of the cooling system being out in the open air means it can also be hit by air strikes, an adversary doesn't need to penetrate the mountain, just take out its cooling.

You'd have to build a fully underground cooling system that goes to a nearby river (or huge lake) and use the cold water from that, which would get costly quick.

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jltsiren 5 hours ago | parent | next [-]

> You'd have to build a fully underground cooling system that goes to a nearby river (or huge lake) and use the cold water from that, which would get costly quick.

Helsinki gets its water from the 120 km Päijänne Water Tunnel, which cost €200-250 million (adjusted for inflation) to build. Peak flow is 10 m^3/s by gravity alone and up to 20 m^3/s with pumps, which should be enough to cool a 1 GW data center. You could increase the cost by 2x (because real wages have gone up), by another 2x (because middlemen have destroyed productivity), and by yet another 2x (because everything is more expensive in America), and it would still be pretty reasonable.

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Brybry 5 hours ago | parent | prev | next [-]

Iron Mountain does it but they used an existing limestone mine with a large water reservoir [1][2]

Edit: I guess the scale isn't comparable to a, for example, Google data center though.

[1] https://www.ironmountain.com/data-centers/colocation/our-dat...

[2] https://betterbuildingssolutioncenter.energy.gov/showcase-pr...

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killerstorm 2 hours ago | parent | prev | next [-]

They already run liquid cooling loops - compute density is way beyond what could circulate through air. Adding more pipes is probably trivial on the scale of datacenter expenses

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walrus01 2 hours ago | parent [-]

Liquid cooling loops don't solve the problem of needing to reject the heat to the atmosphere outside of the building. It just makes it more efficient to transport the heat. At the grossest possible definition, a datacenter of N megawatts on Y acres of land is going to emit the same amount of heat whether it's air cooled equipment or liquid is used to take the heat to the outdoor heat exchanging equipment. On the scale of any very large datacenter the heat exchanging equipment is visible from aerial photos (and from space), take a look at google maps for some of the largest hyperscalers for examples.

	▲	killerstorm an hour ago \| parent [-]
		I assume that "liquid cooling loop" has an endpoint outside of the building which hosts hardware. In this case it's exactly same problem - just make pipes longer. Do you need many acres of land to host a heat exchanger?

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efnx 5 hours ago | parent | prev | next [-]

So they want to build it in space. Trade one heat problem for another, but put it completely out of range (for most attackers).

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martinjc 6 hours ago | parent | prev | next [-]

Pionen in sweden is a datacenter in a bunker. The Pirate Bay used to be hosted there.

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walrus01 5 hours ago | parent [-]

A few racks or even a couple of dozen racks could be called a datacenter, but nothing on any real scale. Enough to host important and niche things? Sure. I was referring more to like the size of what you might see in Quincy, WA.

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jeltz 4 hours ago | parent | next [-]

Pionen is small but it is quite a bit bigger than "a couple of dozen racks". More like 100-200 if I recall correctly.

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jacquesm an hour ago | parent [-]

By 1990's standards that was small. Today it is tiny.

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martinjc 24 minutes ago | parent [-]

In the US the most common deployed size is below 5MW?

Dont know why i can't reply to the person commenting below. But where's the statistics? Who has these datacenters out in the field?

	▲	jacquesm 7 minutes ago \| parent [-]
		Yes, but that's not where the volume is. A 'small' data center, even here in Europe has 100's of racks. There are of course many tiny ones but collectively they don't even add up to one single large Google or AWS DC. Those things will run in excess of 1 or even 2 GW.

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martinjc 4 hours ago | parent | prev [-]

According to their site, Pionen has 1.5MW of cooling capacity https://swedendedicated.com/datacenter/

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testaccount28 6 hours ago | parent | prev [-]

neat. why can't you put the heat in the mountain?

	▲	walrus01 5 hours ago \| parent [-]
		For broadly the same reason that many years of heat from braking has heat-saturated the london underground. https://www.google.com/search?client=firefox-b-d&q=london+un... You could probably drill sideways into rocks and pump heat into the mountain for a certain period of time, but on a multi-month or year time scale, it would catch up with you after you had saturated it.