Patent ID: 6996586

Claim:
A method for reducing an amount of data transferred, comprising: maintaining a first indicator for each source block of data to indicate whether the source block of data has been updated in source storage since lie source block of data was last transferred to target storage; maintaining a second indicator for each target block of data in the target storage to indicate whether the target block of data has been updated in the target storage since the target block of data was overwritten by a corresponding source block of data; maintaining a third indicator for each target block of data to indicate whether a corresponding source block of data or the target block of data is to be retrieved for a stage operation; and when transferring data from the source storage to the target storage, transferring each source block of data for which a first indicator has been set to indicate that the source block of data has been updated; and transferring each source block of data that corresponds to a target block of data for which a second indicator has been set to indicate that the target block of data has been updated.