mount old location as E:
mount new location as F:
robocopy e:\ f:\ /s /e /copy
AT /r:0 /log:c:\temp\copy.log
now you can check copy.log in c:\temp to see what failed to copy.
And if there is any disruptions, running the same command again we only bring over files that are newer in the old location. Also make sure both NAS and the windows machine is on the same switch and 1Gbps to maximize speed of transfer.
It shouldn't take you a few hrs to do this, if you have tons of small files, at worst 48hrs.