2950 III Raid hard drive requirements

Hi all, I have poweredge 2950 III with raid 5 and has 3 fujitsu harddrive in raid 5. Now i would like to add more harddrive to my raid 5 volume. What kind of harddrive is supported in raid 5 by design?

I read it some where that it must be same speed and size. So i am planning to buy same speed and size. But my question is can it be different model or brand? Is different brand or model supported in raid 5 by design? Different brand or model may work but i am not interested in using it if it is not supported by design.

Please let me know if i need to add any more additional information.