Physical redundancy (glossary)
a system resilience principle that states that the system should possess two or more independent and identical legs to perform critical tasks. Jackson (2016)
Jackson, Scott. 2016. "Principles for Resilient Design - A Guide for Understanding and Implementation." In IRGC Rresource Guide on Resilience, edited by I. Linkov. University of Lausanne, Switzerland: International Risk Governance Council (IRGC).
Also called design redundancy by Leveson (1995)