Shared redundancy as a means of producing reliable mission critical systems

We address the concept of "shared redundancy" where one subsystem may compensate for the failure of another subsystem in the design of fault tolerant architectures for mission critical systems. We explore four different design alternatives with varying levels of physical redundancy of the components involved. The analysis shows that the system safety is defined/limited by the "weakest link" among the fault tolerant units, that is, the minimum level of redundancy for all the components that need to work collaboratively will define the system availability.