What is the term for an extra component in a system to ensure availability?

The term for an extra component in a system to ensure availability is known as N+1 redundancy. This concept involves having one additional component above what is necessary to maintain system operation. For example, if a system requires N power supplies to function, an N+1 configuration would include one extra power supply. The purpose is to allow for continuous operation even if one of the primary components fails, thereby enhancing reliability and availability.

N+1 redundancy is crucial in data center design, as it helps mitigate the risk of downtime due to component failure. This proactive approach provides a safeguard, ensuring that there is always a standby component ready to take over if one fails, thus supporting the facility's uptime requirements.

Other choices, while related to system reliability, do not represent the same concept. 1+N redundancy refers to a configuration that relies on one working component with multiple backup components but has a different implication regarding resource allocation. Hot swapping denotes the ability to replace components without shutting down the system but does not specifically address the concept of redundancy for availability. A backup system typically refers to a separate entity that can replace the primary system in case of a failure rather than providing immediate availability assurance like N+1 redundancy does.