From wikipedia: "Matrix RAID utilizes two physical disks. Part of each disk is assigned to a level 0 array, the other part to a level 1 array. This product provides a safe area (the level 1 section) for documents and other items that one wishes to store redundantly, and a faster area for operating system, applications, etc."
The only problem is that "Currently, most (all?) of the other cheap RAID BIOS products only allow one disk to participate in a single array." Which means that this is not possible in Hardware, though "Matrix RAID is a feature that first appeared in the Intel ICH6R RAID BIOS." Which means that it has initially been implemented in hardware. Now, only if this were available on my Hardware RAID controller, or even Software RAID on Linux.