Half the expected bus bandwidth has four plausible causes needing different fixes: a link trained at reduced width, a fabric that never came up, a topology the job did not expect, or a test that measured latency. The sequence of commands that tells them apart, and what each output looks like on a healthy node.
Updated Sep 2026 · Grounded in real AI infrastructure interview loops and written to a senior-engineer editorial bar, with every number worked and every diagram hand-built.
Half the expected bus bandwidth has four plausible causes needing different fixes: a link trained at reduced width, a fabric that never came up, a topology the job did not expect, or a test that measured latency. The sequence of commands that tells them apart, and what each output looks like on a healthy node.
Ranked by how closely each one overlaps this question's topic, so the first card is the thing to read if the answer above moved too fast.
Scored on a diagnostic order that goes from cheapest check to most invasive, correct expectations for each command's output on a healthy HGX node, and the ability to distinguish a hardware fault from a software mapping error from a measurement artifact.
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