Patent ID: 7664793

Claim:
A method comprising: writing first and second data to first and second data volumes, respectively, wherein the first data volume is a first primary volume, the second data volume is a second primary volume, and the first and second data volumes are unrelated data volumes; refreshing the second data volume to the data contents of the first data volume that existed at time T, wherein refreshing the second data volume further comprises overwriting data of the second data volume with data of the first data volume that existed at time T, generating first and second maps in memory, wherein each of the first and second maps comprises a plurality of entries, wherein each entry of the first map corresponds to a respective memory block that stores data of the first data volume, and each entry of the second map corresponds to a respective memory block that stores data of the second data volume, setting a first bit in each entry of the first map, wherein each first bit of the first map is set to indicate its respective memory block stores valid data, and clearing a first bit in each entry of the second map, wherein each first bit of the second map is set to indicate its respective memory block stores invalid data; modifying data of the first data volume while the second data volume is being refreshed to the data contents of the first data volume that existed at time T; modifying data of the second data volume while the second data volume is being refreshed to the data contents of the first data volume that existed at time T; and modifying data of the first data volume after the second data volume has been refreshed.