In-band deduplication for Btrfs

It's unlikely, but it should still not be that difficult to read the data and compare both. For those that don't need the performance hit, that would be turned off and you would remove a dimension from your data structure (btree[hashkey]->bucket->blocks to btree[hashkey]->block).

It should be a performance option. I can think of plenty of cases where for me a hash is fine. In some cases however, I don't really want to play dice with my data. Secondary to that, while right now the possibility of a collision is low, in future things can happen that might change that.

In some cases, depending on scenario, I would rather a system that performs worse than a possibility of a bizarre hidden integrity failure which can make a heck of a mess. If there ever was a hash collision, chances are it wouldn't be detected. The data would just have to be rebuilt and repaired or something. It's just one less vetor to worry about when it comes to big data where integrity is sensitive.