Sizing storage capacity for a global photo backup service launch

You are the product manager for Google Photos, the service that backs up and organizes the pictures people take on their phones. The product is about to launch for users around the world. Estimate, in terabytes, how much storage capacity you would allocate for it. Show your assumptions and your arithmetic. ```hint Break it into a product Total storage is the number of users multiplied by what each user stores. Each of those two factors can be split into smaller pieces that you can reason about with round numbers. ``` ### Clarifying Questions - What period should the allocation cover: the first months after launch, or a multi-year ramp? - Should the estimate include videos as well as photos, and are files stored at original quality or compressed? - Do I count only user data, or also replicas, backups and thumbnails? - Which regions and which user tiers (free and paid) are in scope? ### What a Strong Answer Covers - An explicit equation (users, times per-user volume, times file size) and a stated time horizon. - A funnel for the user count and a segmented model of upload behaviour, rather than one average. - Correct units and arithmetic, ending in a single figure in terabytes. - Overhead beyond raw files: replication or erasure coding, derived files and growth headroom. - A second-angle sanity check and a view on which assumption matters most. ### Follow-up Questions - Which single assumption moves your answer the most, and how would you pin it down with real data after launch? - How would your number change if uploads were compressed rather than stored in original quality? - Why not buy all of this capacity before launch, and how would you phase it?