Transfer from drobo to WD NAS

Im trying to transfer 12TB from drobo to WD NAS through network. Its been failing at some point. Im looking for advice on how to do this as quick and efficiently as possible.
The drobo is in the server room on prem on the network
Im at PC with the USB NAS connected
Ive attempted to drag and drop over but after running for days it looks like its incomplete or failed early.