A medium-sized company with 500 employees has a rapidly growing storage infrastructure with clustered mail， database， and file and print core business applications running on six servers. Using current direct attached SCSI storage pools to each server leads to inefficient utilization of storage space.They also have a backup device attached to each server. They want to consolidate their storage and backup infrastructure into a scalable， high availability and high performance solution. The customer’s top priorities are performance， cost， and availability. Which of the following backup solutions best satisfies the customer requirements？（）