def METHOD_NAME(self):
    """
    start block device mirroring job;
    """
    params = self.parser_test_args()
    target_image = self.target_image
    device = self.device
    default_speed = params["default_speed"]
    target_format = params["image_format"]
    create_mode = params["create_mode"]
    full_copy = params["full_copy"]
    args = {"mode": create_mode, "speed": default_speed,
            "format": target_format}
    if 'granularity' and 'buf_count' in params:
        granularity = int(params["granularity"])
        buf_size = granularity * int(params["buf_count"])
        args.update({"granularity": granularity,
                     "buf-size": buf_size})
    if 'node_name' in params:
        args.update({"node-name": params.get("node_name")})
    error_context.context("Start to mirror block device", LOG_JOB.info)
    self.vm.block_mirror(device, target_image, full_copy,
                         **args)
    if not self.get_status():
        self.test.fail("No active mirroring job found")
    if params.get("image_type") != "iscsi":
        self.trash_files.append(target_image)