How to extend space

Hello World !

I set for my files Directory D:/ (it’s 2 hard disk ~600gb/hdd, with raid, now have 1 TB).If i want, in future to extend this space, how i can do this ?

May be, in the future, i want to add about 4-5 TB Space from 4 hard disks. I can make an option and i will extend the initial space?