US Patent 7165156 Read-write snapshots

A chain of snapshots includes read-write snapshots descending from a read only snapshot. The read only snapshots presents a constant view of the data at the time the read only snapshot is created, and the read-write snapshot starts with the view but can be modified by the user without changing the view of its parent snapshot (e.g., the read only snapshot). Accordingly, the read-write snapshot can be written for various testing purposes while the read only snapshot remains undisturbed to preserve the original data.