Tiered hot-cold storage
Design a tiered hot/warm/cold + archival storage system that automatically moves objects between cost tiers based on access patterns. Constraints: a hot SSD tier (single-digit-ms reads, expensive), a warm HDD tier, a cold/archive tier (minutes-to-hours retrieval, ~10x cheaper), billions of objects, and you must minimize cost while keeping frequently-read objects fast. Cover the tiering engine, access tracking, and retrieval.
What a strong answer looks like
Clarify scale and constraints first. Propose a clean component breakdown, then go deep on the hard parts (data model, bottlenecks, consistency, failure modes) and name the trade-offs you are making.
Clarify4:00 left
Estimate4:00 planned
Design11:30 planned
Deep dive9:30 planned
Failure6:00 planned
Which questions mattered is sealed until you submit. Telling you now would just be handing over the edge cases.
Run or narrate your approach, then ask the coach.