System Resilience and Stability Index Calculator
Calculate the composite System Resilience and Stability Index (SRSI) using redundancy level, mean time to recovery (MTTR), failure rate (λ), and average system load. The index ranges from 0 (no resilience) to 100 (perfect resilience).
Formulas Used
1. Single-Component Availability
A = MTBF / (MTBF + MTTR)
2. System Availability (N parallel redundant components)
A_sys = 1 − (1 − A)N
3. Failure Rate
λ = 1 / MTBF
4. Recovery Speed Score
RSS = 1 / (1 + ln(1 + MTTR)) — logarithmic penalty for long recovery times
5. Load Stress Factor
LSF = 1 − (Load / 100)² — quadratic penalty for high operational load
6. Redundancy Bonus
RB = ln(N) / ln(10) — logarithmic benefit of additional redundant components
7. Composite SRSI (0–100)
SRSI = 100 × (0.35·A_sys + 0.25·RSS + 0.20·LSF + 0.10·RB + 0.10·Diversity)
Assumptions & References
- Components are assumed to fail and recover independently (parallel redundancy model).
- Availability formula follows the standard IEC 60050-191 steady-state availability definition.
- The parallel availability model
A_sys = 1 − (1−A)Nassumes identical, independent components — a standard result from reliability engineering (Billinton & Allan, Reliability Evaluation of Engineering Systems, 1992). - The Recovery Speed Score uses a logarithmic decay to reflect diminishing returns of faster recovery beyond a threshold.
- The Load Stress Factor uses a quadratic model consistent with stress–strength interference theory; high load disproportionately increases failure probability.
- Component Diversity Score is a qualitative input (0–1) reflecting architectural heterogeneity, which reduces correlated failure risk (NIST SP 800-160 Vol. 2).
- Weights (0.35, 0.25, 0.20, 0.10, 0.10) are based on expert-weighted composite index methodology; adjust for domain-specific priorities.
- SRSI thresholds: ≥85 Excellent, ≥70 Good, ≥50 Moderate, ≥30 Poor, <30 Critical.
- References: Billinton & Allan (1992); NIST SP 800-160 Vol. 2 (2021); ISO/IEC 25010 System Quality Model.