Also note how Amazon doesn't claim that the service has 11 nines of data durability, but that it is designed for 11 nines of durability. That's not quite the same.
Backblaze apparently gets the same number by looking at the failure rate of their drives, and how long it takes to recover from a drive failure (reaching the same redundancy as before the failure). By being able to recover from three drive failures before the first drive is rebuilt, they get 11 nines of durability [1]. Or in other words: 0.000000001% of drive failures are non-recoverable and lose data. I assume AWS does basically the same calculation, adjusted for whatever technology they use.
Backblaze apparently gets the same number by looking at the failure rate of their drives, and how long it takes to recover from a drive failure (reaching the same redundancy as before the failure). By being able to recover from three drive failures before the first drive is rebuilt, they get 11 nines of durability [1]. Or in other words: 0.000000001% of drive failures are non-recoverable and lose data. I assume AWS does basically the same calculation, adjusted for whatever technology they use.
1: https://www.theregister.com/2018/07/19/data_durability_state...