Low transfers - copying from my PC in to NAS OMV - where is the bottleneck?

Hi guys,
I am totally new in whole OMV. I build my own OMB based on CPU E8200, motherboard p5Q Se2, 8GB of RAM, 5x 2TB HGST, and 2x1 WD black. System is installed on SSD 32Gb.

When I am copying files via ethernet transfers are about 8Mb/s. I assume it should run faster?

OMV server is plugged in to mikrotik RB3011 (so it's also Gigabit socket).
Where can be a bottleneck? How should I check it?

Thanks in advance,
Daniel.

I figured it out. The problem was... eth. cable . LOL