A global customer’s IT strategy is based upon two DS8000 systems and an N series gateway. They want to protect their  business by implementing a disaster recovery solution. The storage specialist has recommended cascaded mirroring.  Which of the following is the business benefit of cascaded replication（）

• A、it is cost efficient， as a single N series or DS8000 can have its controllers split between the  primary and secondary site and use semi- synchronousmirroring while using asynchronous mirroring to a third site
• B、the second site acts as a repeater station so that greater geographical distances can be achieved
• C、ITprovides high availability together with disaster recovery by implementing Metro/Global Mirror across three geographically dispersed systems
• D、it guarantees data protection by implementing two synchronous copies of the primary site data