Abstract: Snapshots that are consistent across a group of data objects are generated. The snapshots are initiated by a coordinator, which transmits a sequence of commands to each storage node hosting a data object within a group of data objects. The first command prepares a data object for a snapshot. After a data object has been successfully prepared, an acknowledgment is sent to the coordinator. Once all appropriate acknowledgments are received, the coordinator sends a command to confirm that a snapshot has been created for each data object in the respective group. After receiving this confirmation, the coordinator takes action to confirm or record the successful completion of the group-consistent snapshot.

Abstract: Consistent replicas of a data object are created using a replication protocol that includes an opportunistic replication phase followed by a consistent replication phase. During the opportunistic replication phase, dirty regions are selected from the data object included in a primary computer and copied to a data object replica included in a secondary computer according to a selection heuristic. During the consistent replication phase, an immutable image of the data object is created by the primary computer and the remaining dirty regions are copied from the immutable image of the data object to the data object replica to create a consistent replica of the data object.