Oh yeah. That was always a sketchy recomendation, but it sure did make its way around. I think deduplication is remarkably seductive, but doesn't seem worth the cost for almost anyone, given how it's implemented. IIRC, btrfs has a dedup option where you can link up duplicates later, and then you don't have to hold a dedupe table of everything all the time, and don't need to collect writes to check the dedupe table, etc. But rewriting data isn't how zfs rolls, and I get that.