Replication Consistency Groups (RCG), establish the attributes and behavior of the replication of one or more volume pairs. The replication consistency, or write-order fidelity, is maintained for the remote volumes in an RCG.
Before creating RCGs, the replication volumes must exist on both the source and target systems, and they must be of the same size. However, they are not required to reside in a storage pool of the same type, and are not required to have the same properties (such as thick, thin, compressed, or non-compressed). If volumes must be resized, the target volume should be expanded first to prevent disruption in replication.
Since consistency is maintained across volumes of an RCG, it is important to create the RCGs in such a way that they contain either the whole application, or independent components of the application. For example: A complete SQL Server database, including all its data and transaction log disks.
The Recovery Point Objective (RPO) is the maximum acceptable data (in terms of time units), that would be lost in a disaster. RPO is a parameter set by the user, with a value from 15 seconds to 60 minutes. PowerFlex measures the replication lag against the RPO for compliance. While the RPO is set by the user, the replication lag represents the real-time information about how long it took for complete journal-intervals (checkpoints) to arrive to the remote SDR, tracked independently for each RCG. Since each journal internal represents a point of data consistency for that RCG, the lag represents in real-time the potential data loss if there is a disaster, while the RPO is measured against it for compliance.