Highly redundant architecture
Dis a stint there a few years ago.
There architecture is highly redundant.
Two data centres with a complete redundancy in each data centre.
I.E. four times the hardware they need for peak load. So they certainly did not skimp on the cash.
Still there is always something unforeseen that will prevent failover.
2 hours downtime in fifteen years is not so bad. Just a few months short of 6 sigma.