Patent ID: 6957362

Claim:
A data storage system for providing access to a production dataset and at least one snapshot dataset, the data storage system comprising storage containing the production dataset and the snapshot dataset, the snapshot dataset being the state of the production dataset at a point in time when the snapshot dataset was created, the data storage system being programmed for instantaneous restoration of the production dataset with the state of the snapshot dataset by initiating read/write access through a foreground routine to what appears to be a restored version of the production dataset while the production dataset is being restored by a background routine, the foreground routine keeping a record of data blocks that have been modified by the read/write access through the foreground routine since initiating the read/write access through the foreground routine, the background routine copying data blocks from the snapshot dataset to the production dataset if said record of the data blocks indicates that the data blocks have not yet been modified by the read/write access through the foreground routine since initiating the read/write access through the foreground routine.