Patent ID: 7313578

Claim:
In a data processing network having a production site, first and second remote sites, a first communications link between the production and first remote sites and a second communications link between the first and second remote sites wherein the production site includes a magnetic disk storage device and a host adapted to update the data in the magnetic disk storage device, wherein the first remote site includes a first data store that mirrors the data in the magnetic disk storage device, a second data store that operates in a first mode to mirror the data on the first data store and a copy program, and wherein the second remote site includes another data store, the data processing network being characterized by a method for providing a backup of the data at the production site in each of the first and second remote sites by: A) establishing in the first remote site first and second tables for recording the occurrence of any change in the data in first data store and a third table for recording the need for any transfer of data from the second data store to the data store in the second remote site; B) initially establishing a state during a second operating mode whereby the data in the data store in the second remote site corresponds to the data in the first data store at a point in time; C) reestablishing the first operating mode for the second data store by combining information in the first and third tables to identify the changes made to the first data store while the second data store was operating in a second operating mode; and D) differentially splitting, after synchronism is achieved between the first and second data stores, the second data store from the first data store by: i) copying the information in the second table to the third table; ii) clearing the second table; and iii) enabling the copy program to transfer the changed data in the second data store to the data store in the second remote site, whereby the data store in the second remote site is brought into synchronism with the data that existed in the first data store at the time of said differential splitting.