I'm in the process if transferring / duplicating the contents of my old DNS-323 to a new DNS-340L.  Each of these NAS units currently contain a single Seagate ST3500320AS 500GB drive (both were previously in the DNS-323).  Before setting up the new NAS I transferred all the data on the old NAS onto one of the drives and moved the empty drive over to the new NAS.  I have no intention of using a RAID setup.
At this stage until the drive in the new NAS reaches capacity (it will be around 2/3 full), I will leave the old DNS-323 as a standby backup offline and disconnected.  Going on from there I may continue to leave it that way if I decide to purchase additional new drives.
Anyway I wanted to ask about the best / fastest way to transfer the drive contents from the old NAS to the new one.  They are both connected via a gigabit ethernet switch and/or router.  I am currently copying the data one root folder at a time using "copy"/"paste" using two file browser windows on my Windows 10 machine.  There's about 20 root/parent folders totaling about 300 GB of mixed data and at this rate I'm getting an average speed of 10 MB/s (20MB/s peak) according to Windows.  Assuming each folder is a similar size I'm about 1/4 done already.  I'm not in any particular hurry, but I did wonder if there's a faster way to perform this copy process?  I know it seems to take a lot longer to copy many small files than fewer large files.