According to what I shared in a different thread..
There is theoretically only 6 for the internal SSDs. At least on the 300 series mainboard.. I just learned this last night and was a bit disappointed about it as I planned to swap mainboards. Means I will have to swap my 2230 from internal to the expansion bay to not be throttled on speeds. The new mainboad only has 16 where as the original has 20.. I’m not entirely sure how all everything was allocated yet but it’s definitely less.