1. A storage system comprising: a plurality of first switches, each of the first switches connected to at least one storage cluster of storage nodes of a plurality of storage nodes, each of the storage nodes containing randomly placed replicas of data objects; and a second switch that connects the plurality of first switches to at least one of each other or a root switch to form a tree-like structure, the plurality of storage nodes to replace a lost replica of a data object by replicating a replacement replica from a source replica of the data object, and placing the replacement replica in the storage cluster that contains the source replica according to a non-global replacement policy and to replace an additional lost replica of an additional data object by replicating an additional replacement replica from an additional source replica of the additional data object in the storage cluster, and placing the additional replacement replica in the storage cluster or an additional storage cluster that is connected to the storage cluster by a switch.