cluster design

Both carry RDMA at 400Gb/s; the decision is about loss behavior, tuning burden, and who operates it. A defensible recommendation with the conditions that flip it, the format this question is scored on.

One synchronous job, 16k GPUs, and any single component can stall all of them. The blast-radius analysis interviewers want: which faults take down a rack vs the run, where the shared single points of failure hide, and how parallelism layout maps onto failure domains.