System designHardsd-g599

Subject Blob storage dedupLevel Senior–Staff~40 minCommon in Storage & CDN interviewsIndustries Technology

Question

Design a blob store with global deduplication for a backup/sync product (think Dropbox-style file storage). Constraints: petabytes stored, high duplication across users (same OS images, shared documents), block-level dedup with variable-size content-defined chunking, 10 nines durability, and you must never lose a block that is still referenced. Cover chunking, the dedup index, and reference lifecycle.

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.