Patent ID: 7000145

Claim:
A method for applying changes back to an original copy of data to reduce an amount of data transferred, comprising: maintaining a first indicator for each block of data in a first storage to indicate whether the block of data has been updated in the first storage since the block of data was last transferred to a second storage; maintaining a second indicator for each block of data in the second storage to indicate whether the block of data has been updated in the second storage since the block of data in the second storage was overwritten by a corresponding block of data in the first storage; maintaining a third indicator for each block of data in the second storage to indicate whether a corresponding block of data in the first storage or a block of data in the second storage is to be retrieved for a stage operation; and upon receiving a reverse restore operation, transferring each block of data in the second storage for which a second indicator has been set to indicate that the block of data has been updated to the first storage; and transferring each block of data in the second storage that corresponds to a block of data in the first storage for which a first indicator has been set to indicate that the block of data in the first storage has been updated to the first storage.