https://blog.synology.com/data-durability
> Data durability: the ability to keep the stored data consistent, intact without the influence of bit rot, drive failures, or any form of corruption. 99.999999999% (11 nines) durability means that if you store 10 million objects, then you expect to lose an object of your data every 10,000 years.
Edit: and it'll still break when us-east-1 is destroyed by the sun exploding.
Shouldn't that be multiplied by the number of bytes of this object? I still don't quite understand the math apparently because then we'd all be losing 10KB+ files yearly.
For the purposes of this calculation, you would probably use the average size of a stored file, determine the number of chunks that was split into, and then the likelihood of losing/corrupting a chunk.
By looking at the durability of objects, you (a) reinforce the object-store nature of S3, and (b) avoid reporting “durability per kb”, which isn’t linear, and more difficult to interpret.
Honestly, the durability number is so high, that adding the bytes as a unit would just make it difficult to reason about. And S3 doesn’t store “bytes” — it stores objects (made of bytes). So, that’s the metric they chose to focus on.
* have a bad block on one drive * have a bad block in *EXACTLY SAME LOCATION* on the second drive * have a bad block in *EXACTLY SAME LOCATION* on the third drive * all of that happening within one scrub period (which is usually once a month).
And that's just simple RAID6 setup without external redundancy.
As you can see it would be far easier to lose data due to just correlated drive failures, than from random block corruption.