Another important question these days is the capabilities of the drives and the controller (most controllers do share the bandwidth to some degree between the SATA ports), and why using solid state drives isn't an option. For example, striping mechanical hard drives will almost always still provide poorer performance than a single SSD. Especially seeing as modern SSDs can easily saturate a 6Gb SATA link. For ultimate performance, you'd connect a fast SSD to either a SATA Express port, or a bespoke PCIe controller.
I just can't help but think that RAID-0 is a lot more redundant these days than it used to be. Faster performance, increased risk of data loss, 2 drives required, or just slap a fast SSD in instead. Unless of course you need lots and lots of storage, and even then you can now get 1TB SSDs for less than £60...
EDITED: 28 Dec 2015 12:31 by DAVE!!