So much facepalm here. A Backblaze rep is in that thread confirming that they do have a failure case where they can lose backup data -- or at least, it'll become inconsistent. Ok, that's bad. I don't think they're idiots, but it'd be interesting to know what's so technically challenging about the index problem that they haven't been able to solve it.

But ... 17 TB total? For online backups? That's just not what they're designed for, unless you've got one hell of an internet connection. The complainant says it's going to take over a year to re-upload the 13TB. That's insane.

I think you have to give up on online backups for that use case and settle for a pretty beefy home rig in a fire-resistant box. Moving that kind of data up and down an internet connection just doesn't work real well yet.