[forum456]

I am aiming for 50T but raid-2...my machine learning data is expanding fast.

there is no point to keep big data if it is for self learning.
most of the time, after you have learnt, you have no practical use of the data.
even your machine learning knowledge is very specialised and has no practical use unless your work/job requires it.
it is learning for learning sake or hobby sake. 

are you keeping the data for commercial use ?