Most of the Thunderbolt-equipped storage devices on the market employ arrays of mechanical hard drives. Not Promise's Pegasus J2, which is being billed as the fastest one of them all. This external drive combines a pair of SSDs to enable transfer rates as high as 750MB/s. Rather than using 2.5" solid-state drives, the J2 is loaded with a pair of smaller mSATA drives, allowing the whole thing to be stuffed into a tiny case measuring 2.9" x 4.3" x 0.8". Total weight: just 140 grams.
Promise doesn't provide any details on the controllers or NAND used in the component SSDs. However, it does indicate that the dual drives are configured in a software RAID 0 array by default. Users can opt for RAID 1 and JBOD arrays instead, but those won't deliver the full 750MB/s. Indeed, neither will powering the J2 with a standard Thunderbolt cable. To reach top speed, the Pegasus J2 needs to draw auxiliary power from a wall socket. The J2 is capable of running on Thunderbolt power alone, but Promise doesn't say how much performance is sacrificed by ditching the adapter.
Although the power adapter is included with the Pegasus J2, a Thunderbolt cable is not. You'll need to provide your own, which adds about $50 to the J2's already steep asking price. The 256GB model sells for $800, while the 512GB model costs an arresting $1500. For reference, a couple of 256GB mSATA drives will set you back less than $600 at Newegg. Most of the mSATA drives Newegg has in stock come with three-year warranties, but the J2 is covered for just two years. That seems a little stingy for such a premium device.
Right now, the Pegasus J2 supports Mac OS X only. I expect Intel will encourage Promise to add Windows support, but there aren't that many PCs out there with Thunderbolt ports right now.