In general, the subject matter described in this disclosure can be embodied in methods, systems, and program products. A system includes a first data center, a second data center, and a third data center. The multiple data centers are configured to replicate a logical collection of data that comprises multiple logical partitions of data. The system comprises a first writing subsystem that is designated to write updates to a copy of a first logical partition of data that is stored by the first data center. The system comprises a second writing subsystem that is designated to write updates to a copy of a second logical partition of data that is stored by the second data center. The system comprises a third writing subsystem that is designated to write updates to a copy of a third logical partition of data that is stored by the third data center.