RAID works on many diffrent drives and works very well.

However, the "green" edition drives from Western Digital are energy-saving hard drives that unfortunately does not spool up consistantly.  The speeds of the drives can range from 5400 RPM to 7200 RPM at any given time. 

Because RAID requires a mirrored, consistent response from both drives, the green edition drives may have a delay between the two drives during read/write access. This may eventually lead to an unhealthy or corrupted array.