cooling

Start from the power envelope, because it decides the GPU count more often than the budget does. The scalable unit that makes the design a copy of a known-good one, the four networks, and the three line items that gate the schedule while everyone is discussing GPUs.

Four separate facility limits have to be cleared and total building capacity is not one of them. Power per rack, heat rejection, floor loading and network reach each fail independently, and each has a different remedy with a different lead time. The options that exist, priced, and the one that is usually taken.

The GPU board power is about 60 percent of the answer. The rest is CPUs, memory, NICs, fans, switches, thousands of transceivers and the cooling plant, and each is a term people leave out. The full derivation, the term that surprises everyone, and the contracted number that is larger than all of it.

Every watt in comes out as heat, so the design starts from the load and one equation. The flow rate, the CDU count and redundancy, the water quality requirements that decide whether the loop survives three years, and the automatic response that has to fire before a human can read the page.

Three approaches with overlapping ranges, and the choice is decided by the facility and the service model rather than by thermodynamics alone. Where each runs out, what the middle option buys that people underrate, and the operational cost that comes with the most capable one.

A fixed power envelope turns hardware selection into an optimization with one objective and several overheads competing for the same watts. Where the 1 MW actually goes, why the answer is not simply the most efficient GPU, and the two overheads that can be cut to buy more compute.

Doubling per-rack density is four separate upgrades with different lead times, and the electrical one usually cannot be done while the hall runs. The phasing that keeps capacity available through it, the constraint that decides whether it is possible at all, and the number that says whether to upgrade or move.

A whole rack failing at once is a shared dependency, which narrows the causes to four before anyone touches anything. What the out-of-band network tells you in the first minute, why the order of restoration matters, and the decision about liquid cooling that has to be made before power returns.

700 W per GPU is the number everyone knows and it is only 40% of the answer. The chain from GPU TDP to node, to IT load, to facility power with PUE: about 1.8 MW, and what that means in racks and dollars.

Throttling is the hardware protecting itself, so it produces no error and no failure, only a job that is quietly slower. The two telemetry fields that name it, the arithmetic linking clock to throughput, and why the response differs completely depending on whether the cause is one node or the room.