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.