就HDS官方文件解釋為：replication／mirror
主要功能如下：

1. Uses local mirroring technology to create and maintain a full copy of any volume in the storage system.
2. Create one or more copies of a data volume within the same storage system.
3. Use ShadowImage copies as backups, with secondary host applications, for data mining, for testing, and other uses — while business operations continue without stopping host application I/O to the production volume.
4. Enables nearly instant point-in-time recovery from data corruption or data loss compared to non-disk based solutions such as tape- or vault-based recovery

以上皆由Hitachi官方所釋出的[]ShadowImage® User Guide](http://www.hds.com/assets/pdf/vsp-hitachi-shadowimage-user-guide.pdf)截取，希望有解決樓主您的疑惑