3DC cascade configuration
In a multi-target configuration, data is copied from the primary site to two secondary sites. As shown in the following illustration, the TC P-VOL is the primary production volume in a 3DC cascade configuration. The TC secondary site is located at a short distance from the primary site.
The host issues an update to the TC primary volume (P-VOL), which is copied synchronously to the S-VOL. The UR system copies the synchronous S-VOL data to the UR secondary site.
Data in the UR S-VOL is an asynchronous copy of the TC P-VOL. Depending on RPO and bandwidth, UR S-VOL data can be very close to P-VOL data. As always with UR, data consistency is ensured.
Failure recovery occurs as follows:
- If a failure occurs at the TC P-VOL, business continues because data in the UR S-VOL is restored to the primary storage system using the intermediate volume, if needed. Update sequence integrity is ensured.
- If a failure occurs at both TC P-VOL and S-VOL, an implemented disaster recovery plan would re-direct host activities to the UR S-VOL.
For recovery information and procedures, see the section "Recovery for 3DC UR/TC cascade configuration" in the Universal Replicator User Guide.