Storage controller should be able to handle 8x sata, it can handle more?

Hey everyone,

I have a question regarding the HP Smart Array P410 that's comes shipped in the HP Proliant DL 180 G6. It is stated in the specs that it can handle 8 sata disks, but the case itself has twelve hotswap bays. Both the raid controller and FreeNAS (a linux distribution) can see and use all twelve disks. Thus my question is: What does the 8x sata mean then?

Kind regards,

S.