Cost, realizability and scalability of the highly reliable fault-tolerant computers are the main issues which bother the development and limit the wide deployment of these computers. However, the development of fault-tolerant computers based on hardware and software resource of commercial-off-the-shelf (COTS) computers has advantages over traditional proprietary fault-tolerance design techniques, and will become the research hotspot. However, there are two important and difficult problems, i.e., the ...