I transfered about 4TB of data and was annoyed my transferspeeds were not as advertised. I get 10Gbit can be hard to reach depending on system, and this was only mechanical drives, so I had some understanding...but still.
Then I noticed the connection I used was the wrong network, so I used my onboard ethernet instead of my NIC...and my switch was limited to 100mbps bandwidth...
After changing the IP of the network drive it was a big difference