def METHOD_NAME(self, root_dir, ori_filename, tar_filename, timeout=20):
    """dd file in snapshot"""
    self.session = self.main_vm.wait_for_login()
    self.file_info = self.files_info[0]
    ori_file_path = "%s/%s" % (root_dir, ori_filename)
    tar_file_path = "%s/%s" % (root_dir, tar_filename)
    dd_cmd = self.main_vm.params.get(
        "dd_cmd", "dd if=%s of=%s bs=1M count=500 oflag=direct")
    mk_file_cmd = dd_cmd % (ori_file_path, tar_file_path)
    try:
        self.session.cmd(mk_file_cmd, timeout=timeout)
    except ShellTimeoutError as e:
        self.main_vm.verify_status("io-error")
        self.file_info.append(tar_filename)
    else:
        self.test.fail("Can dd large file on a small space")