Reliability requirements
Capture concurrent-maintenance and single-component-fault requirements, then identify the state, path, transfer, loading, independence, common-mode, recovery, workload, and contract evidence still needed before topology selection.
Reliability topology requirements
Project topology requires named maintenance and fault states, the exact affected path, transfer interruption, post-event loading, path and control independence, common-mode dependencies, a recovery SLO, and workload and contract consequences. These two choices are useful requirements, but they cannot select N, N+1, distributed-redundant, 2N, a Tier, or a capex premium. Compare and price candidate designs only after that project evidence closes → Ch 12.1.
Worked decision — stated assumptions
All ledger inputs are assumed teaching values chosen to exercise this chapter’s method; they are not market quotes, OEM performance claims or operating records. Arithmetic uses the full entered precision.
| Input | Value |
|---|---|
| Concurrent maintainability required? | yes |
| Ride through one component failure? | yes |
Decide which reliability requirements to carry into the design brief. Assume the owner requires both concurrent maintenance and ride-through of one component failure. The test is Boolean: Yes / Yes yields Required / Required. The topology result remains “Not determined from these two requirements.” Hold topology selection and pricing until named isolation/fault states identify the exact paths, surviving capacity, interruption, independent controls and workload recovery consequence.
Change the fault requirement to No while keeping maintenance at Yes. The fault requirement becomes “Not required by this screening input”; the crossover is the owner's acceptance of workload interruption on an unplanned component fault. That relaxes the design brief and accepts that service consequence. It does not select an N+1 or 2N topology or certify a Tier. Chapter 12.5 owns the state-by-state acceptance method.
Guide derivation. Method and handoff: Chapter 12.5 — Quantitative Reliability & Availability Modeling (RBD / FTA / Monte-Carlo).
These are transparent screening estimates, not final designs, financial advice, or project approvals. Replace every default with current project data and have the responsible project authorities validate the result. You can save, share a permalink, or export to CSV; see the full calculator suite.