Sharded, encrypted storage between friends over Yggdrasil

> only lets the original writer delete a shard.

That makes sense on the very surface, but eventually someone's going to lose their config, and all their orphaned storage is just occupied forever in the rest of the group.

I'm pondering an "anti-challenge" primitive, whereby storing nodes can ask the original writer to confirm that it still has the stub file. (Because if that's lost, the data can't be decrypted anyway, there's no point to still saving it.) And if that fails for X months in a row, sorry, time to go. Or maybe raise it for manual review so the node operator can check in with the others before pushing the "reclaim storage" button.

Very interesting concept. This has also already been implemented in Tahoe LAFS (www.tahoe-lafs.org) but for some reason it was never really adapted for something that scales beyond local networks. I always thought that this would be an awesome idea since a lot of people already operate their own NAS, oftentimes with spare disk space that could be used as intended by this project, but don't want to pay additionally for some cloud provider for a decentralised backup.

How do you prevent storage exhaustion attacks if a "friend" decides to dump encrypted garbage on your peer node?