Raid 5 provides redundancy like Raid 1 but doesn't take as much "redundant space". Naturaly, it is less secure than Raid 1.
If you have 5 drives, Raid 1 creates duplicates on all 5 drives. So ur total capcity is just that of one drive = C GB.
If u use Raid 5, the capacity will be 4xC GB. The last drive is used for redundancy. If one drive fails, you can retrive it. If 2 drives fail, Raid 5 is useless where Raid 1 would still work.