How do I set up external storage for my domain backups?
Under your domain dashboard, click on Backup & Restore. Once there, click on the Remote Storage Settings button at the top of the page. You should see a space labeled FTP (s) Not configured. Click on that, and you will come to a form where you will provide the IP of your external storage, the directory path for where your files will be stored, and your FTP username and password for your external storage.
You also have the choice to use Passive Mode and FTPS (both checkboxes). Once you have specified the necessary information, click OK, and Plesk will try and connect to the external storage. You will see a green notice above indicating a successful connection, which will indicate that your remote storage is now set.
See video under How do backups work?