Can you mix hard drives on a RAID setup?

[KDOG]

I have a IBM 14GXP in my system right now (7200rpm, ATA66) and I was thinking of adding another for a RAID but do I have to use the same one or can I mix and match?

 

[kranky]

I believe you can mix them, but if the HD sizes are different it will only use the amount of space on the smaller drive. For example if one drive is 20GB and the other is 30GB, you'll waste 10GB on the bigger drive.