As far as I know, for RAID 5 you have to delete the array (which destroys the data) then rebuild the array. This has to do with the way the stipes & parity are distributed across the array. Although I think on some higher end, dedicated hardware systems there might be a way around this.
Personally, I'd copy the system partition to the velociraptor, I think Ghost can do this. Then, back up the data, rebuild the array, and good to go.