System designMediumsd-g601

Subject Storage tiering hot coldLevel Mid–Senior~35 minCommon in Storage & CDN interviewsIndustries Technology

Question

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.

Learn the concepts

Narrate your design

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Run or narrate your approach, then ask the coach.