code: def create_backup(self):
          
  
          js = json.dumps({'cmd': 'backup'})
          params = urllib.urlencode({'json': js})
          answer = self._read(self.api_url + 'cmd/system', params)
  
          return answer[0].get('url')
docs: Ask controller to create a backup archive file, response contains the path to the backup file.
  
          Warning: This process puts significant load on the controller may
                   render it partially unresponsive for other requests.