Design deduplicated file storage on filesystem
Overview
This question evaluates system design and storage engineering competencies, including multi-tenant isolation, authentication and authorization models, content-addressable storage and deduplication, reference counting and garbage collection, concurrency control, API surface design, and scaling across nodes using only filesystem primitives.
Google
Sep 6, 2025, 12:00 AM
Software Engineer
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System Design
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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.
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Define and justify the following:
- Authentication and authorization (who can upload, read, delete).
- Object naming and tenant namespace layout.
- External APIs (upload, get, delete; optionally list, head, copy).
- Content-addressed storage and deduplication strategy.
- Reference counting and garbage collection.
- Consistency and concurrency semantics under concurrent uploads/updates/deletes.
- 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.
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