Protection or Redundancy: Which is Better and When in Terms of Mean Time to Failure and Cost

Abstract

This article is about comparing the effectiveness of protection mechanism and redundancy methods in terms of mean time to failure and cost criteria. Under the protection mechanism, a component is assumed to have different failure rates when it is protected and nonprotected. The protection block is also subject to failure and has constant failure rate. Alternatively, a redundant component which has the same failure rate with the original component may be used to enhance the reliability. For single unit and series systems, necessary conditions on the failure rate of the component are obtained to have a relation between the mean time to failure values of the system under both protection and redundancy. The extension of the results to coherent systems is also discussed.