What a missing nine costs you
A year is 31,536,000 seconds. Availability figures are a percentage of that number, which is why two specifications that look almost identical on a datasheet describe completely different operations.
Seven ninesis what Stratus ztC Endurance is rated for. Bars are scaled logarithmically — on a linear scale the last four rows would be invisible.
Redundancy is not the same as failover
A failover cluster notices a fault, then restarts the workload somewhere else. That gap is the outage. Fault-tolerant hardware never has the gap, because the second copy was already executing the same instruction.
What a cluster does after a fault — minutes, and whatever was in flight is lost.
What fault-tolerant hardware does instead — the surviving half simply carries on.
Transactions lost when a component fails on a correctly sized system.