NAS326 copy external drive to another external drive

That can certainly be done, using the command line. You can enable the ssh server (somewhere in network settings) and login over ssh.

Then you have to find the mountpoints of the disks. These are in /e-data, so the command

ls /e-data/

will give you the mountpoints. Then enter the empty disk:

cd /e-data/<some-hex-code>/

and copy the contents of the other disk:

cp -a /e-data/<hex-code-of-the-other-disk>/* .

You can find which disk is which by looking at the content:

ls /e-data/<some-hex-code>/

Then there is one nasty detail, the copy session is connected to the terminal it's running in. So when you close the terminal, the copying stops. To prevent that, you'll have to decouple it:

cp -a /e-data/<hex-code-of-the-other-disk>/* . 2>&1 >output.txt

This will redirect stderr to stdout, and stdout to the file output.txt. When everything works, you can see the contents of the disk being copied via the webinterface or samba, and the file output.txt growing with command output.