Technology is disclosed for backing up and retrieving data in a distributed backup system (“the technology”). Files of a user can be stored across multiple computing devices (“the devices”) of the user, e.g., mobile devices, and/or at a server, e.g., a cloud storage server, in the distributed backup system. The user can define various policies for storing different files at different devices. For example, the user may define a policy for storing video files on a device that has a bigger display. The devices can be used as an edge cache of the distributed backup system in serving files to the user. Upon receiving a request for retrieving a file, the technology determines if any of the user devices that are in proximity to the requesting device has the file. If yes, the file is transmitted to the user from the proximate device instead of from the server.