Too slow on MacPro 2013

Connected to the Thunderbolt port on the Drobo 5D works, but not with 2 * 10GB / s.
Overall, I use 4 * 4TB WD Black drives and SSD (mSATA Crucial 120GB).
The maximum performance is in test
Disk Speed ​​Test Write at about 181 MB / s and read 199 MB / s
Xbench test at about 348 Write MB / s Read and 104MB / s. When uncached Read there are dramatic declines of 2 MB / s.
Conclusion: In the system selection note that Thunderbolt is fully supported, otherwise the RAID system is well suited for data archiving.