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
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