Reducing Uncertainty About Common-Mode Failures

Multi-version programming is employed in fault tolerant computer systems in order to provide protection against common-mode failure in software. Multi-version programming involves building diverse software implementations of critical functions. The premise of building diverse versions is that the likelihood of a programming error in one version causing a failure in an identical manner as an error in another version is reduced. Skeptics of multi-version programming have correctly pointed out that common-mode failures between redundant diverse versions can reduce the return on investment in creating diverse versions. To date, other than using historical data from other projects, there has been no way to estimate the potential for a given multi-version programming system to suffer a common-mode failure. This paper presents an algorithm and software analysis prototype to reduce the uncertainty of whether software flaws in diverse versions can result in common-mode failure. The analysis uses software fault injection techniques to subject one or more versions to anomalous behavior. From this, we can predict how the software will behave if real faults exist in the multiple versions.