Dell R410 / H700 / RAID1 performance issue

Hi all,

I have a Dell R410 with a PERC H700 in RAID1 with 2x 18TB SATA drives but the write performance is terrible (around 20MB/s).

Attached is the how they Virtual Disk has been configured. The server is receiving Hyper-V replication and both the server sending and this one receiving have ample network capacity (1Gbps ports).

The drives both show as 6Gbps (which they are), but I'm not sure where I'm losing the performance, surely it should be better than 20MB/s? The server is not doing anything else other than receiving the Hyper-v replicas, so no other activity utilising the disks.

Any help or pointers in the right direction would be greatly appreciated.

Thanks in advance.