I'm planning to develop reliability and maintainability study for data centers since it is required by the client. My method of developing this study is by using fault tree analysis. However, I am stuck with the fundamentals of Boolean algebra and not quite sure which approach to use. Below is an example
Assuming there are 2 redundant system, let's call them System 1 and System 2. These 2no. systems both have components A, B and C. These components are assumed to be identical for both System 1 and System 2 (A1, B1, C1 for System 1 and A2, B2, C2 for System 2).
Diagram below shows the approach I have used.
Which of the following fault tree above is the more appropriate representation of overall critical failure?