Description of the illustration rep_request

The illustration shows a local data center with the primary database DB-a that is serviced by a Recovery Appliance, RA-x. The remote data center has a standby DB-a that is serviced by RA-y. The primary RA-x has a solid arrow to RA-y to indicate active replication with RA-y to support the standby DB-a and allow it to fully recover its databases. The remote RA-y has a hollow arrow to RA-x to indicate request-only replication to RA-x.

When RA-x is offline such as for planned maintenance, the backup pieces are re-directed to the remote RA-y. When RA-x is back online, the backup pieces received by RA-y but missing on RA-x while it was offline are requested by RA-x. Thus, the replication network traffic is only for missing pieces to restore RA-x's ability to fully recovery its databases.