Patent ID: 7725672

Claim:
In a data storage environment having a first volume of data denominated as the source being stored on a data storage system, and a second volume of data denominated as the clone and which has data content that is a copy of the data content of the source being stored on the data storage system or on another data storage system, a method of protecting the clone's data content during a restoration of the source while making data from the clone instantly available through the use of a Copy on Demand Engine (COD), the method comprising the steps of: restoring the source by copying data content from the clone to overwrite the data content of the source in a copy on demand process; receiving host I/O request from the source; placing the request in a COD Queue; having the COD Engine copy the required data from the Clone to the Source to allow the host I/O request to be processed; tracking the changes between the Source and the Clone; and preserving the data content of the clone by not allowing it to be overwritten by host writes during the restoring step.