A storage system, such as a file server, creates persistent consistency point images (PCPI) or “snapshots” that are point-in-time representations of the storage system. The storage system uses persistent consistency point images to backup or mirror data. Using data already found in the data block...http://www.google.com.tw/patents/US7984085?utm_source=gb-gplus-share專利 US7984085 - Rate of change of data using on-the-fly accounting
