WD DX4000 NAS - How do I copy large volume data to it?

If old drive is already in a USB caddy, connect that. Otherwise, network is the option.

I don't think you can put any old hard drive in your NAS.  I would not.

Put the hard drive in a computer (direct connect will be faster than USB) and copy over a network. Make sure you use Wired and not Wireless and Gigabit connections.  

It will take a while. In my setup, connecting by Ethernet, I can copy 150 GB of virtual machines to the other computer in under an hour, so you are probably looking at about 4 hours to do the copy above.

The NAS has a raid and would see it as foreign drive.  The best way to migrate the data is to use a tool like robocopy

Usually NAS formats the disks to Linux like format....so simply copy the file from the old disk to the NAS and forget about tricks....i made some trick sometime ago.....0.5 TB gone

So John, 150GB in 1 hours!! thats only 40MB/sec??? would expect to get a bit faster than that! (50-60MB/s)

I am going by recall in terms of speed, but my point was that 700 GB will take a while:  2.5 to 4 hours in that range.