Durable object store
Design the storage layer of a durable object store (S3-class) targeting 11 nines of durability for exabytes of immutable blobs, optimized for cost. Objects range from tiny (KB) to huge (TB), the workload is write-once-read-many, and a fraction of objects are read constantly while most are nearly cold. Design the on-disk layout, the redundancy scheme, the metadata/index, and how you achieve the durability target affordably.
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.
Clarify5:30 left
Estimate5:30 planned
Design16:30 planned
Deep dive13:30 planned
Failure9:00 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.