Fault Tolerance
A system's ability to keep running correctly even when some components fail.
Fault tolerance is a system’s ability to keep operating correctly even when one or more components fail. Azure achieves it through redundancy at multiple layers: duplicate power and network hardware within a datacenter, data replication across Availability Zones in a region, and geo-redundant storage that copies data to a paired region hundreds of miles away. The key exam distinction is from high availability: high availability minimizes downtime and targets an uptime percentage, while fault tolerance goes further, aiming for zero perceptible disruption when a failure occurs. It is closely tied to eliminating single points of failure.
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