The 1GB ram per TB is wrong. More memory definitely helps, especially if you add an L2ARC cache which can use a lot of memory just for mapping. But in most case

The 1GB ram per TB is wrong. More memory definitely helps, especially if you add an L2ARC cache which can use a lot of memory just for mapping. But in most cases you are probably fine with just 1-2GB of ram. I would never use deduplication on ZFS, it is very slow even if you have enough RAM. And in most cases, savings are less than 10%.