Back-of-the-envelope estimation

How this question breaks down

1. 1Numbers to knowCore21 minThe handful of latency, throughput and size anchors that let you reason about a design in orders of magnitude before you measure anything.
2. 2QPS and storageCore20 minTurn a user count into requests per second at peak, a read/write split, and the bytes the system must keep for years, showing every step.
3. 3BandwidthCore19 minConvert request rates and object sizes into bits per second in and out, then size each tier's fleet by whichever resource runs out first.

Work through the parts in order and you’ve covered the full design. Each part is one topic.