Patent ID: 8843721

Claim:
A method, comprising: maintaining a data storage system comprising a controller, a first lower performance storage medium and a second higher performance storage medium, the controller coupled to the first and the second storage mediums and arranged to control I/O access to the first and the second storage mediums; storing an image comprising a plurality of regions of data on the first storage medium, initiating a copy function to copy one or more regions of the plurality of regions of data stored in the image on the first storage medium from the first storage medium to the second storage medium, in response to an IO access to the one or more regions of the plurality of regions of data stored in the image on the first storage medium, directing further I/O accesses for the image first to the second storage medium and then to the first storage medium, periodically aging data from the second storage medium to the first storage medium, creating a new empty bitmap for a plurality of periods of time, and in response to an I/O access for a region of data in the image, updating a latest bitmap to indicate that the region of data has been accessed and updating a previous bitmap to indicate that the region of data has not been accessed.