System design interview questionHardCollaborative System
Design a File Storage Service like Dropbox
Design Dropbox-like file storage: upload/download files, list folders, sync metadata across devices.
Interview scope
Split metadata vs bytes: App + DB for metadata; Object Storage for files; CDN for downloads; Client never talks to DB/object store without App/signed flow.
Functional requirements
- Upload and download files.
- List folders / file metadata for a user.
- Share links or permissions at a basic level (high-level is enough).
Scale and quality goals
- File bytes belong in object storage — not as BLOBs in your primary SQL for large files.
- Metadata (name, path, owner, versions) in a database.
- Uploads/downloads should scale via edge/CDN where possible.
Capacity assumption
Design for this scale
Assume ~10M users, average ~15 GB stored per user → order of ~150 PB total (back-of-envelope). Peak uploads matter for the app path.
Practice more than a diagram
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