obtaining mirrored data so that the original data can be recovered after failure without transmitting the entire mirrored data between computers . a write request at a primary computer is stored in a delay buffer and a copy is transmitted to a backup computer , where it is stored in a delta queue . the backup computer executes the copy of the write request to the mirrored data and transmits an acknowledgement to the primary computer that the copy of the write request has been received . in response to the acknowledgement , the primary computer executes the write request stored in the delay buffer . the computers send to each other subsequent acknowledgements of the write request execution , enabling the computers to delete the write requests . if the primary computer fails , the primary computer can recover the original data by receiving only the copies of write requests that remain stored in the delta queue .