Do you enabled Caching on the RAID controller?

We have the same performence issue with replication and failover.

IOMETER: (OpenPerformenceTest - Max Throughput 100% Read )
500 GB LUN, Block, Test on a Hyper-V Server

IOPS, MBPS, Response Time
Only one SAN, 17368.182502,542.755703,3.263848
with Replication: 15586.519347,487.07873,3.664976
with Failover: 15373.858457,480.433077,3.790156