recently Had this epiphany. Make the Pi do the work instead of my main system.
After looking around, I found rsync was the choice for copying files from one mass storage device to another. This is per much Linux searching. I was unable to find specifically RPI stuff. Moving around 600+ GBs from one USB 3.0 drive(transfer from) to a USB 2.0 drive (receiving) is very slow.
SSH into the pi "sync -av /from /to"
The USB 3.0 drive is NTFS formatted as a back up drive.
The USB 2.0 was cleared and formatted as ext4. (sacrifice drive)
This is still going on after 3+ hours and just over 50% maybe.
Up Next! How should I improve this process?
The next step is to clear out and change the USB 3.0 drive into ext4 and use it as the NAS storage.
The intent for the USB 2.0 drive will be to backup important items like essential documents from the NAS.