Patent ID: 7447860

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, which has a data content that is a copy of the data content of the source being stored on the data storage system, a method, operable on a computer system, for protecting the clone's data content during a restoration of the source, 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, while allowing host reads and writes to the source during the restoring step, said copying being determined by a clone delta map, used to track extents of the clone that are different between the clone and the source, and a protected restore map, used to track extents of the source that are modified during the restoring step, when an indication is set in the clone delta map and not set in the protected restore map; preserving the data content of the clone by not allowing it to be overwritten by host writes during the restoring step; recording information that indicates the source affected by a host write in the protected restore map; and setting the protected restore map as the delta clone map after the restoring step is completed.