[TylerE]

One thing I will suggest: you’re assuming failures are non-correlated and have an equally weighted chance per in it of time.

Neither is a good assumption from my experience. Failures being correlated to any degree greatly increases the chances of what the aviation world refers to as “the holes in the Swiss cheese lining up”.

[mixermachine]

You are 100% correct. Heavily depends on where the servers reside. Just a rough estimate for the case that the failures are non related.