99% uptime is 3.65 days down a year

transcript

Your service is up 99 percent of the time. Sounds great, right? Hold on. That's 3 point 65 days of downtime. Every single year.

Count it in minutes. 99 percent is over 5,000 a year. That's called low availability. Add one nine. 99 point 9 percent, the standard. 8 point 76 hours.

See the pattern? One nine cut the downtime by ten. And it keeps going. Every nine, another ten times.

Four nines, high availability. 52 point 6 minutes a year. Five nines, mission critical. 5 point 26 minutes. That's the whole year.

So here's the trap. You run at 99 point 9. Someone asks for 99 point 99. Sounds like a tiny bump. Your yearly budget drops from 8 point 76 hours to 52 minutes.

That isn't ten percent better. It's ten times less room to fail. Every year. One more nine. Ten times less downtime.

Full breakdown in the lecture.