You should always copy data to WHS via the network share, i.e.
\\server\music. This is normally done from a client.
(Doing this from the server desktop is possible, but unsupported. And you are right, that adding a disk to the storage pool would reformat the disk.
Or do you mean the backup function in the console?
In this case (given all updates are installed on the server) you can add the disk as backup disk and perform the restore via console.
Best greetings from Germany
Olaf