Design a File Storage Service
Last updated: February 19, 2026
Quick Overview
Design a real-time file storage system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
DoorDash
February 19, 20261
9
652 solved
Design a real-time file storage system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
ML system design at DoorDash goes beyond model selection. This Technical Screen question evaluates your ability to design end-to-end ML pipelines, from data collection to model serving, while considering production constraints like latency and reliability.
What the Interviewer Expects
- Define clear ML objectives with appropriate loss functions and metrics
- Design a comprehensive feature engineering pipeline
- Discuss model selection with trade-offs (complexity vs interpretability vs latency)
- Plan online and offline evaluation strategies including A/B testing
- Address serving infrastructure: batch vs real-time, latency requirements
- Consider data quality, labeling strategy, and feedback loops
Key Topics to Cover
How to Approach This
- Start by clarifying functional and non-functional requirements with the interviewer.
- Estimate the scale: QPS, storage, bandwidth. This drives your design decisions.
- Draw a high-level architecture first, then deep dive into 1-2 critical components.
- Discuss trade-offs explicitly (e.g., consistency vs availability, SQL vs NoSQL).
- Address failure scenarios, monitoring, and how the system handles 10x traffic spikes.
Possible Follow-up Questions
- How would you handle the cold start problem?
- How would you debug a model that works well offline but poorly online?
- How would you handle a 10x increase in prediction requests?
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Requirements
Functional Requirements:
- File Upload and Download: Users should be able to upload files of various types (images, documents, etc.) and download them on demand.
- Real-time Access: The ...
Capacity Estimation
Assuming DoorDash has approximately 30 million users, and each user uploads an average of 1 file per week:
- Daily Uploads: 30M users / 7 days = ~4.3M uploads/day.
- File Sizes: Assuming an av...
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