Some SCSI hardware RAID controllers do something similar to this with RAID-1, but I've never seen it attempted with two hardware arrays over software. The proprietary implementation for a single controller, that I use, is known as RAID-1E and consists of 2 RAID-0 arrays as the logical disks of a RAID-1 array. I've also seen redundant controllers, but they're limited by controller manufacturer and backplanes. For sheer speed, a four disk RAID-0 array will be faster as deathstar13 suggested.