3 ms·

>The chance they can recover all their data is only (1-0.003)^100000... Which means every customer suffers data loss :-( You just made the same mistake you're

>The chance they can recover all their data is only (1-0.003)^100000... Which means every customer suffers data loss :-( You just made the same mistake you're criticizing. You assumed the 100K files were uniformly and independently spread. They're also likely clustered, and perhaps not even at the same data center. Given the variety of drives Backblaze uses, the drives are also not likely to all be the same model, so your failure method is also unlikely. You also only looked at the case there are exactly 16 good drives. The proper failure estimate is 1 - (odds of 17 good + odds of 18 + odds of 19 + odds of 20). I'm not sure where you got the 20 x 19 x 18 part either. Did you mean 30 choose 16 or something like that? Using the proper 1-... method I get 0.00267, not 0.03.

londons_explore 8y ago
>You just made the same mistake you're criticizing Yes. Even if you take it into account, the vast majority of customers will see data loss, assuming random (but not even) shard distribution. I rounded and approximated to avoid explaining too many probability rules... As you can see, it gives the same result at the end.
- ChrisLomont 8y ago
  >it gives the same result at the end No, it doesn't. You picked 3% of all drives failing out of the blue. Your next estimate was an order of magnitude too high. Your last assumption of p^# drives is not reasonable. The proof is in reality. Backblaze has run over a decade, with all sorts of hardware failures, server configs, running many drive models through their lifetime, across manufacturers, across technologies, across multiple datacenters, and had not seen the level of failures you claim they will. So I suspect their method of estimating is more accurate than yours. So far it matches reality much better.