As explained earlier, PowerFlex uses asynchronous replications and reports the replication lag and RPO compliance. The replication lag signifies how far behind (in seconds) the remote target data is from the source, while the RPO provides a compliance measurement for the lag to comply with. 

Since the target is a few seconds behind the source volumes data, after an unplanned outage at the source and failover of operations at the target, the database at the target opens with data as-of the last journal update. For PowerFlex replication, this update is typically a few seconds behind the replication source, based on the replication lag.

Note: Typically, a planned failover scenario is different than the unplanned because, in a planned failover the database is first shut down on the replication source, the replication synchronizes the latest changes, and then either a failover is performed (making the target read-writable), or switch-over (swapping the roles of the replication source and target). In either case, there is no loss of data because the database was shut down first.

PowerFlex replication creates a full disaster protection solution for the replicated database. Replicating user databases is often sufficient, but, by replicating the system databases, all database patches and changes from the source site are replicated to the target. In addition, PowerFlex snapshots can be taken at the remote site to provide additional copies of the replicated data for testing, development, and reporting.  

See the use cases in the next section for deployment examples.