Hi,
I was and still am a bit confused by the difference between "local" and "remote" NAS backups as they are used here, but I learned that to backup one 320 to another one on the same network, you use the "remote" backup application. You do not need to start up the FTP service and ignore the port forwarding info on the GUI. If you are on the same network, you just use the 192.168.0.XXX or whatever your remote NAS IP is. Then "browse" to the location for the backup. One step to do first, is to go and enable the "backup server" on both of the 320's otherwise, the test will only fail even if your IP and folder settings are correct. You can only back up at the folder level not "Volume". If you have a bunch of folders, you might try to reorganize them into a larger group under one folder or be ready to do a lot of backup entries.
If you are backing up one 320 to another 320 on a different network via the internet, I do not know the answer, perhaps some other reader can give you the answer. Good luck