Over the weekend I've been trying to setup Gentoo with on a server whose motherboard was advertised as having on-board RAID 0 and RAID 1 functionality. It turns out that the 'RAID controller' is in fact an extension of the BIOS that, when accessed using a special device driver that you have to add to the operating system, gives you RAID functionality. The OS can still see the seperate disks in the array and the user is trusted not to access them directly. Madness.
More info here.
I wasted a day messing around with this, trying to get it running using Device Mapper only to find out that the chipset I have isn't supported yet.
I've ordered a 3ware SATA RAID card. It does proper RAID. Watch this space..
