Just add another drive, you don't really need RAID. you can RAID two drives with different sizes, but the size will be of the least amount of space. ex: you have 1TB and put an 2TB beside it. you'll only use 1TB+1TB. to setup a RAID you'll need to erase all hdds. RAID0 is for performace, with the risk of loosing data if a drive fail, because the data is split in half between hdds. In RAID1, this is for backup, you mirror your hdd on another one. you have 1TB+1TB, you only use 1TB. for the rest of the RAID configuratons you'll need 3+ drives. If you really want speed, go for an SSD, if storage, just add another drive.