1. A method of attaching user storage to a central storage management system, the method comprising: receiving a first request to attach a first cloud-based user storage to the central storage management system; receiving a second request to attach a second cloud-based user storage to the central storage management system; accessing the first and second cloud-based user storages and determining, respectively, first and second sets of objects stored therein; and for each object in the first and second sets of objects, storing corresponding metadata in the central storage management system, wherein the metadata indicates the cloud-based user storage at which the corresponding object is stored.