Walk through the ZeRO stages and FSDP internals. Where does the memory actually go and when is it gathered?
ZeRO and FSDP both shard training state across data-parallel ranks, but the trick is in when each shard is gathered and freed. Get the memory accounting and the all-gather timing and you can size any run.
Updated Sep 2026 · Grounded in real GenAI, LLM, and AI/ML engineering interview loops and written to a senior-engineer editorial bar.
ZeRO and FSDP both shard training state across data-parallel ranks, but the trick is in when each shard is gathered and freed. Get the memory accounting and the all-gather timing and you can size any run.
Lead with where the obvious approach breaks, because that is the judgment they are screening for — most candidates jump straight to the happy path and lose the room.
Then walk the failure back through the pipeline in order, naming the one metric the customer's exec sponsor actually cares about before you propose the fix.
