Resiliency vs Redundancy: What’s the Difference?

Resilience and redundancy offer ways to yield a dependable system—known as system dependability. Both resilience and redundancy are critical for the design and deployment of computer networks, data centers, and IT infrastructure. Despite the critical nature of both, resiliency and redundancy are not the same thing.

In this article, we’ll explain system dependability, the differences in resiliency and redundancy, and how they both contribute to your system’s dependability.

What is system dependability?

System dependability is defined as “the trustworthiness of a computing system which allows reliance to be justifiably placed on the service it delivers”. A computing system and its components must be strong enough to consistently deliver its service to end users.

A key attribute of dependability is the reliability of the system, so that the rendered service is available throughout its operating duration at an acceptable performance level. Both resilience and redundancy help achieve a system’s dependability, but they are not interchangeable strategies.

Resiliency and redundancy

In the domain of computer networking, resilience and redundancy establish fault tolerance within a system, allowing it to remain functional despite the occurrence of issues such as power outage, cyber-attacks, system overload, and other causes of downtime. In this context, the terms can be defined as follows:

• Redundancy is the intentional duplication of system components in order to increase a system’s dependability.
• Resilience refers to a system’s ability to recover from a fault and maintain persistency of service dependability in the face of faults.

With these definitions, redundancy and resilience are not interchangeable but complementary: Redundancy is required to enhance a system’s resilience, and resilience of individual system components ensures that redundant components can recover to functional state following a fault occurrence. Redundancy is an absolute measure of the additional components supporting system resilience, whereas resiliency is a relative (and continuous) measure of the impact of fault on the system operation.