1. A method comprising: connecting a host computer to a cluster of storage servers attached to storage devices, the host computer having a byte addressable, persistent memory configured to store data in a region; organizing the storage devices attached to the storage servers as a replication group for the region; changing the data of the region at a byte-addressable granularity; selecting a storage device of the replication group to receive the changed data; and storing the changed data on the selected storage device to efficiently replicate the changed data at the byte-addressable granularity.