Durability vs Availability
Two different storage guarantees — whether data survives, and whether it can be reached right now — routinely conflated because both are quoted in nines.
Durability is the probability that stored data is not lost. Object storage services commonly quote eleven nines, achieved by replicating each object across devices and facilities and continuously verifying checksums.
Availability is the probability that a request succeeds now. The same service typically quotes three to four nines — six orders of magnitude lower.
The distinction matters because they fail differently and are protected differently. Durability protects against media failure and bit rot; it does not protect against you deleting the object, a bad deployment overwriting it, ransomware encrypting it, or a credential being compromised. Eleven nines of durability means the provider will faithfully preserve whatever you told it to store, including the wrong thing.
Which is why versioning, object lock, cross-account backups and delete protection exist as separate features: they defend against the failure modes durability explicitly does not cover, and those are the failure modes that actually happen.
The practical instruction: never treat a durability figure as a backup strategy. The question to ask of any storage tier is not "how durable is it" but "what happens if the wrong thing is written, and who could delete this?"