How Thermal Management is Changing in the Age of the Kilowatt Chip
An anonymous reader shares a report: As Moore's Law slowed to a crawl, chips, particularly those used in AI and high-performance computing (HPC), have steadily gotten hotter. In 2023 we saw accelerators enter the kilowatt range with the arrival of Nvidia's GH200 Superchips. We've known these chips would be hot for a while now -- Nvidia has been teasing the CPU-GPU franken-chip for the better part of two years. What we didn't know until recently is how OEMs and systems builders would respond to such a power-dense part. Would most of the systems be liquid cooled? Or, would most stick to air cooling? How many of these accelerators would they try to cram into a single box, and how big would the box be? Now that the first systems based on the GH200 make their way to market, it's become clear that form factor is very much being dictated by power density than anything else. It essentially boils down to how much surface area you have to dissipate the heat. Dig through the systems available today from Supermicro, Gigabyte, QCT, Pegatron, HPE, and others and you'll quickly notice a trend. Up to about 500 W per rack unit (RU) -- 1 kW in the case of Supermicro's MGX ARS-111GL-NHR -- these systems are largely air cooled. While hot, it's still a manageable thermal load to dissipate, working out to about 21-24 kW per rack. That's well within the power delivery and thermal management capacity of modern datacenters, especially those making use of rear door heat exchangers. However, this changes when system builders start cramming more than a kilowatt of accelerators into each chassis. At this point most of the OEM systems we looked at switched to direct liquid cooling. Gigabyte's H263-V11, for example, offers up to four GH200 nodes in a single 2U chassis. That's two kilowatts per rack unit. So while a system like Nvidia's air-cooled DGX H100 with its eight 700 W H100s and twin Sapphire Rapids CPUs has a higher TDP at 10.2 kW, it's actually less power dense at 1.2 kW/RU.
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