Methods, systems, and apparatuses, including computer programs encoded on computer-readable media, for receiving a write request that includes data and a client address at which to store the data. The data is segmented into the one or more storage units. A storage unit identifier for each of the one or more storage units is computed that uniquely identifies content of a storage unit. A mapping between each storage unit identifier to a block server is determined. The mapping is sent to a plurality of metadata servers to provide the mapping in case of failure of the metadata server. For each of the one or more storage units, the storage unit and the corresponding storage unit identifier is sent to a block server. The block server stores the storage unit and information on where the storage unit is stored on the block server for the storage unit identifier. Multiple client addresses associated with a storage unit with the same storage unit identifier are mapped to a single storage unit.