Why too optimistic? Probably closer to 4 9s. With this outage of ~2 hours, we are at ~99.97% for this year. (I am not aware of any other downtime during 2021)

Why too optimistic? Probably closer to 4 9s. With this outage of ~2 hours, we are at ~99.97% for this year. (I am not aware of any other downtime during 2021) Rule of thumb (I strongly prefer minutes/year instead of 9s, to get an immediate sense of how good the availability is): 99.9% : down for 525 minutes / year, or roughly ~10 hours 99.99% : down for 52 minutes / year, or roughly ~1 hour 99.999% : down for 5 minutes / year