Performance Problems

I had an external RAID5 array attached via USB 3 to a Windows 10 PC and I could get 220 MB/s read and write performance.

I attached this same RAID5 array to a computer (ROCK64 = 4 x Core ARM chip with 4GB RAM) running OMV3 via USB 3. This OMV3 computer is connected to my other computers via Gigabit Ethernet.

Using SMB/CIFS I get 90 MB/s read and write out of my RAID5 array (40% of the performance).

Using NFS I get 12 MB/s read and write out of my RAID5 array (5% of the performance) unfortunately I have a linux application that only works over NFS).

I expected to loose a little performance going over a network and through another computer, but nothing like this.

Since I have a UPS in Windows 10 I chose the device option to improve the USB performance: "Enable write caching on the device" and "Turn off Windows write-cache buffer flushing on the device"

In OMV3 is there a way to check the underlying performance of the RAID5 array to take the network out of the equation?

In OMV3 is there a way to improve the performance of USB devices?

In OMV3 is there a way to improve the performance to something acceptable, especially the NFS?

I added async to the NFS share options which has doubled the performance to 24 MB/s. I know async isn't recommended, but I do have a UPS.

I setup NFS on a different linux distribution (Ubuntu) than what OMV3 is based on to check NFS performance and it is just as bad...is NFS just a slow protocol?