def connect
      log("connect")
      ret = Lib::Rados.rados_connect(handle)
      raise SystemCallError.new("connect to cluster failed", -ret) if ret < 0
    end
def connect
      log("connect")
      ret = Lib::Rados.rados_connect(handle)
      raise SystemCallError.new("connect to cluster failed", -ret) if ret < 0
    end
helper methods below