If you’re running TrueNAS, the replication feature was the smoothest and easiest way to move large amounts of data when I did it 18 months back. Once the destination location was accessible from the sending host, it was as simple as kicking off a snapshot, resulting in a fully usable replica on the receiving host. IIRC, IXsystems staff told me rsync can be problematic compared to the replication/snapshot system, as permissions and other metadata can be lost.