Redundant Software Functions vs Common-Mode Failure
Mandate diverse algorithm and execution-environment independence for safety-critical software redundancy to eliminate common-mode failure exposure.
CyberTRIZ analysis · Space contradiction RMA024 · one of 8,235 worked contradictions published by CyberTRIZ.AI
Regulations
Business Context
Duplicating critical software functions can provide backup capability when one execution path fails. However, redundant instances based on identical code, requirements, algorithms, development tools, or assumptions can fail simultaneously when exposed to the same defect or unexpected condition. Additional software copies may therefore create apparent redundancy without true independence.
Space TRIZ Resolution
Critical software redundancy should include functional diversity where common-mode failure represents significant mission risk. Different algorithms, independent validation paths, simplified backup logic, separate execution environments, or dissimilar monitoring mechanisms can provide alternative means of achieving essential functions.
Applicable TRIZ Principles
Principle 1 – Segmentation separates critical software functions into independent execution paths.
Principle 13 – The Other Way Round uses an alternative method to verify or provide the same essential function.
Principle 40 – Composite Materials combines different software approaches within one fault-tolerant architecture.
Expected Outcome
Greater software fault tolerance
Reduced common-mode failure exposure
More credible functional redundancy
Improved recovery from unexpected software defects
Decision Indicators
Early indicators include:
Redundant computers execute identical software without independent protection.
One software defect can affect all backup channels.
Backup algorithms depend on the same assumptions as primary algorithms.
Software redundancy is measured primarily by the number of copies.
Common-mode software failures receive limited verification attention.