Patent ID: 7178055

Claim:
A method of ensuring data consistency after a failover event in a redundant data storage system having a first data storage facility that initially acts as a primary facility for storage requests and a second data storage facility that initially acts as a secondary facility for the storage requests, the method comprising: conditioning the second data storage facility to assume the role of the primary facility in response to a failover event, the second data storage facility being disjoint from the first data storage facility; and conditioning the first data storage facility to assume the role of the secondary facility, including sending a copy of data committed at the second data storage facility to the first data storage facility as a batch wherein the copy of data includes a version of data committed at the second storage facility, the copy of the data committed at the first storage facility as a whole; wherein the copy of the data committed at the second facility is represented by a log file record of write transactions, within the log file at least one first write transaction is removed in light of a subsequent write transaction affecting the same data.