Design deduplicated file storage on filesystem

Q: Design deduplicated file storage on filesystem

This is a System Design interview question from Google for Software Engineer roles. View the full question and solution on PracHub.

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Question

System Design Task: Filesystem-Only, Multi-tenant, Deduplicated File Storage

You are asked to design a multi-tenant file storage service with the following constraints and requirements:

Only OS filesystem APIs are allowed (e.g., directories/files, permissions, hard links/symlinks, atomic rename, file locks, fsync). No databases or external KV stores.
Users belong to tenants; tenants must be isolated from each other.
Identical files must be deduplicated.
Define and justify the following:
1. Authentication and authorization (who can upload, read, delete).
2. Object naming and tenant namespace layout.
3. External APIs (upload, get, delete; optionally list, head, copy).
4. Content-addressed storage and deduplication strategy.
5. Reference counting and garbage collection.
6. Consistency and concurrency semantics under concurrent uploads/updates/deletes.
7. Scaling across multiple storage nodes (sharding, replication assumptions, routing).

Assume a POSIX-like environment supporting atomic rename, hard links, advisory file locks, and SHA-256 hashing.

Design deduplicated file storage on filesystem

System Design Task: Filesystem-Only, Multi-tenant, Deduplicated File Storage

Solution (Locked)

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