Abstract: The invention is a method and apparatus for mirroring and relaying computer data to improve continuity of data by maximizing the distance between two copies of the data in synchronous mode, zero data loss environments. In one embodiment, the invention uses multiple remote mirror sites to increase the distance of one copy of mirrored data from another copy of mirrored data. In another embodiment, the invention uses relays in a wide-area cascade to increase the distance of a remote mirror site from a server sending write requests. This is done without affecting system performance by allowing the server to continue performance when an acknowledgment is received from the first relay, without waiting for an acknowledgment from the remote mirror site.

Abstract: Loss of synchronization, due to a digital data signal having the same signal value for an extended number of bit or symbol periods, is overcome through the use of a coding scheme which assures transitions after each such period despite the absence of transitions in the signal to be encoded. Broadly, within the encoder, a digital input signal having m signal levels is transformed into a coded digital output signal having n possible signal values, where m<n. The transformation alters the current digital input signal value as a function of the previous coded digital output signal value and the current digital input signal value performed in a number system whose modulus is n. In a disclosed embodiment, a binary input signal is coded into an output signal having three signal levels.