Availability design quality refers to the capacity of a system or infrastructure to remain operational, minimizing downtime, and ensuring continuous service delivery, especially in the event of a failure. The concept of N + 1 redundancy ensures that if one component fails (such as a host or a power supply), there is always an additional, spare component available to take over the workload, maintaining the system's availability.
N + 1 redundancy in a vSphere cluster means that the cluster has enough resources to tolerate the failure of one host without affecting the availability of the workloads. This setup provides high availability and resilience in the event of a host failure.