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4.2Reliability design
Covers the five RASIS metrics for measuring system reliability, availability calculation for series/parallel configurations, and the distinctions among fault tolerant, fail-soft, and fail-safe behavior under failure, learned through cost-versus-reliability tradeoff judgments.
When a system architect designs redundancy, the simplistic idea that "duplicating a component brings peace of mind" is not enough, because how the components are connected (in series or in parallel) determines the overall availability via an entirely different formula. Furthermore, how a system should behave the instant a failure occurs—continue operating fully, degrade its functionality, or stop safely—has a different optimal answer depending on business requirements. This section builds the judgment to weigh a target level of reliability/availability against cost when choosing a configuration, grounded in the RASIS metrics, series/parallel availability calculation, and the three behavioral patterns under failure.
4.2.1The five RASIS metrics
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