Mac Pro: RAID 1 controller

It's software based, and is performed through Disk Utility. Fine for a level 1 array though, and will save you some cash (though I do prefer to use a controller myself).

Adaptec will NOT work for OS X, as they don't make drivers for it. Even if they did, it would also need EFI firmware in order to boot.

If you want a hardware RAID card that boots, take a look at Areca (be sure the model does have EFI bootable listed in the specs - some haven't in the past, though that's been changing). The least expensive would be an ARC-1210 (standard SATA ports), and locate the boot drives in the empty optical bay. A couple of others to consider would be Atto Technology and Highpoint (RR43xx series, which is ODM'ed by Areca - but Highpoint's support sucks).

Beyond that, I'd need more information to help you (i.e. model year of the MP, as there may be an adapter needed - '09 systems do - to use the HDD bays with an SFF-8087 port based card).

Hope this helps.