docs: def raid_alert(self, status, used, available, type):
          """RAID alert messages.
  
          [available/used] means that ideally the array may have _available_
          devices however, _used_ devices are in use.
          Obviously when used >= available then things are good.
          """
          if type == 'raid0':
              return 'OK'
          if status == 'inactive':
              return 'CRITICAL'
          if used is None or available is None:
              return 'DEFAULT'
          elif used < available:
              return 'WARNING'
          return 'OK'