It’s still hard to get used to this spectacle: we take a powerful server and immerse it in a tank of liquid, then apply voltage and hope that no sparks fly. But maybe we should be afraid of something else: continue to build data centers with a service life of more than 10 years, the cooling of which depends solely on air flows? How sustainable is an industry that spends more on providing electricity to rotating fans than it does on powering processors?
“Immersion cooling is when the server is completely immersed in a dielectric liquid,” explained 3M engineer Jimil Shah at the Facebook Open Compute Project Virtual Summit 2020 conference in may. “With immersion cooling, we can significantly increase computational density compared to air cooling systems.”
Over the past few years, vendors have repeatedly pointed out that immersion cooling can both increase computing density, improve energy consumption, and extend the life of existing hardware (you could make your investments work several years longer if you put servers in a kind of stable stasis). But the argument for extending the service life is irrelevant. We do not equip existing servers with immersion cooling. But we know that if we go beyond the limits of acceptable heat generation, in the future it is impossible to design processors in this way. In other words, when we need to increase computing power, we have to think about the ultimate computational density.
“We have come to the conclusion that servers need to be reinvented,” said Mark Shaw, General Manager of advanced hardware at Microsoft. “Racks, power, servers, internal components — everything needs to be changed.”
The topic of liquid cooling was a red line throughout the OCP Summit conference, which lasted a day and a half. Three years after we schematically described the frightening picture of a server being submerged in a tank of mineral oil, immersion cooling has turned from a carnival show into a real science.
At the conference, we heard a number of good news, thanks to which we now have a more confident view of the future of submersible cooling. Here are the three news items:
• developed a diving chassis. Before that, we took and loaded existing servers designed for air cooling systems. But the air and the liquid is a different environment. The special standardized chassis for submersible servers being developed within the framework of OCP will have a length comparable to the length of a refrigerator door and a thickness comparable to the thickness of a chocolate bar, which, when fully equipped, will weigh no more than 34 kg;
• new dielectric fluids have been created. Production of new liquids for immersion cooling is ready. And this is not a mineral oil, but artificially created hydrocarbon and Fluorochemical compounds that have a lower boiling point compared to H2O. The emissions of the gas bubbles are essentially tiny tanks for the transport of heat. Such liquids allow you to create tanks with continuously boiling contents, effectively cooling the servers immersed in it. At the same time, these new liquids evaporate and condense so quickly that the server extracted from the tank is not only cold, but also dry;
• maintenance methods have been developed, and it is easier to maintain a stable environment. Air flow is a non — constant medium. A liquid tank, by contrast, provides a stable environment for servers, in which sensors more accurately determine physical characteristics, which in turn are much easier to stabilize. The robotic arm created by Asperitas, which is attached to a service cart, can remove a specific chassis from the tank and move it to a kind of desktop for maintenance.