Raid is a method to stripe or mirror data over multiple drives. Raid 0 is not technically raid, but increases performance by splitting the data between two drives minimum but if a drive fails you lost all. Then on reads you get two drives speed delivering the data. Raid 1 is a mirror, a 1:1 copy for data safety no performance increase, but you save your data if one fails, replace the drive and it can rebuild the mirror. Raid 5 is a parity stripe, it takes 3 drives. data goes onto 1 and 2 and a parity bit on 3, then the next block of data goes on 2 and 3 and parity on 1, and then the next bit goes on 3 and 1 and parity goes onto 2. This gives the stripe speed with a one drive fault tolerance, you can replace a bad drive and the parity rebuilds the array. so the speed of two drives at the cost of one third of the storage capacity.
But for simplicity the m,2 pci express x4 drive for the OS, games, and programs and a 2tb sata hdd for storage and downloads would be easier and better.