With the third party transfer protocol,USN achieves the following objectives: Managed centrally by a metadata server,USN can make users share its storage space dynamically,so USN is used effectively;

• 采用三方传送协议实现USN可以达到以下目的:元数据服务器集中管理存储设备实现了存储空间的动态共享,提高了存储空间的利用率;