Patent ID: 7024530

Claim:
A method for establishing a point-in-time copy, comprising: generating a source relationship data structure and target relationship data structure when establishing a point-in-time copy relationship between source and target storage areas, wherein the source and target relationship data structures each include an indicator for each source storage area and corresponding target storage area in the point-in-time copy relationship; initializing the source and target relationship data structures to set the indicator for each source storage area and corresponding target storage area in the point-in-time copy relationship to a first value; determining that data was written to one target storage area after establishing the point-in-time copy relationship; setting the indicators to a second value in the source and target relationship data structures corresponding to the source storage area and corresponding target storage area in response to determining that the data was written to the corresponding target; receiving a request to update one source storage area included in the point-in-time copy relationship; if the indicator in the source relationship data structure for the source storage area to update is the first value, then determining whether the indicator in the target relationship data structure for the target storage area corresponding to the source storage area to update is set to the first value; if the determined indicator in the target relationship data structure is the first value, then writing the data in the source storage area to update to the target storage area; and applying the update to the source storage area after writing the data in the source storage area to the target storage area if the determined indicator in the target relationship data structure is the first value.