Max IO throughput

We have a  Poweredge servers r740xd with PERC H740P controller, 2x 6242 Xeon processors and 768GB memory runniing ubuntu 18.04 and have 7 readintensive 8 TB SAS drives rated at 1.2GBps 

But when running FIO even with 200 jobs, I am not able to get more than 5GB/sec throughput.   Are there any recommendations on tuning the system for higher IO throughput

Thanks