I just got OMV installed on a 4GB Raspberry Pi 4 (I.e one with true gbit ethernet and USB 3), with 2x8TB WD Red drives attached via USB 3.
My plan is to share one of the drives, and have OMV rsync to the other nightly.
I was disappointed with the SMB transfer speed, especially on macOS. Further reading suggest that's down to signing, but it still seems a bit slow on Linux. I tested a few things to be clear where the bottleneck is:
iperf3 : 900mbit
wget (serving with Python from the RPi4): 112 MB/s
scp: 44 MB/s
smb macOS client: 29 MB/s
smb Linux client: 82 MB/s
So transfer via wget and iperf shows me that neither the disks nor the network (wired on both ends) are the problem.
I've read scp can be slow on RPi (even the 4) as the encryption is intensive.
I'd be pleased though to improve on the SMB speed - there shouldn't be that much overhead surely?