Universal Principles of Design, Updated and Expanded Third Edition

156 Redundancy

Using backup or fail-safe elements to maintain system performance in the event of failure.

Redundancy is the most reliable method of preventing catastrophic failure. The principle applies widely across a range of contexts, including archiving, communication, design, engineering, software, staffing, etc. For systems requiring high reliability, there should be no single points of failure — i.e., all critical elements should have backups of some type.1

There are four basic types of redundancy:

1. Mixed redundancy — When causes of failure cannot be anticipated and the consequences of failure are catastrophic, different kinds of redundancy should be considered — e.g., having both a hydraulic and a mechanical brake. Mixed redundancy ...