If you add a drive, the WD software has some fancy code that make it a RAID 5. Just pop the drive in and follow the instructions on the LCD.
This is what I read, I will be testing it later this week.
Also, this will only work with the SAME Enterprise drives. 2TB or 3TB drives. Only 3 models exist. Check the WD Dashboard for specifics.
If you put any other drive in the server, you will get a message on the LCD.
[http://homeservershow.com/forums/index.php?/topic/3537-dx-4000-supported-drives/page__p__35864__hl__dx4000__fromsearch__1#entry35864](http://homeservershow.com/forums/index.php?/topic/3537-dx-4000-supported-drives/page p 35864 hl dx4000 fromsearch 1#entry35864)