Patent ID: 8140772

Claim:
A system for maintaining a plurality of data storages coherent with one another for redundancy purposes, said system comprising: a first data storage system coupled to a first transaction processor for handling input and output transactions, and coupled to a wide area network; a second data storage system coupled to a second transaction processor for handling input and output transactions, and coupled to the wide area network; said first transaction processor permitting a first data write transaction to occur with respect to data within the first data storage system; said second transaction processor permitting a second data write transaction to occur with respect to data within the second data storage system; said first transaction processor permitting the second data write transaction to occur with respect to data within the first data storage system only upon data consistency between the first and second data storage systems being validated wherein the first data write transaction and the second data write transaction are defined by a sliding window of input/output operations; and said second transaction processor permitting the first data write transaction to occur with respect to data within the second data storage system only upon data consistency between the first and second data storage systems being validated.