Can you partition a pair of drives so that part of your storage is striped, and part mirrored? For example, would OS X's RAID tools allow the following? * Two 500 GB drives. * 250 from each are STRIPED to make a fast 500 GB volume. * The remaining 250 from each are MIRRORED for use as a 250 GB backup destination. * Total storage 750 GB: 500 fast, 250 redundant. Or can something similar be done? I'd love to get the speed of striping, but if one drive fails all is lost. So setting aside some backup space for work-in-progress would be great. TIA!