Promise was the first to get us a Thunderbolt chassis with the Pegasus R4/R6. Not only was the Pegasus the first shipping Thunderbolt storage chassis, but it continues to be among the fastest on the market. If you've never seen one, the Pegasus R4/R6 is a 4 or 6 bay 3.5" external storage array with built in RAID and Thunderbolt controllers. Promise doesn't ship a chassis without drives, so you get to choose from between 4TB in the lightest configuration (4 x 1TB drives) at $1050 all the way up to 18TB (6 x 3TB) in the beefiest $3000 config. Sequential IO performance is great, generally hitting around 700MB/s for a 6-drive RAID-5 array. There's room for improvement, but running several drives in RAID-0 is typically not the best idea for redundancy.

The biggest issue with the Pegasus (other than cost) is that it doesn't ship with solid state drives. Although the use of 3.5" mechanical hard drives results in good sequential performance and great capacity, random IO performance suffers. After all, even a single SSD tends to have an order of magnitude better random IO performance than a hard drive. For most Thunderbolt use cases (e.g. tossing video/audio/photo work), the Pegasus' array of hard drives is fine. The world is clearly moving towards solid state storage however, and with LaCie offering an SSD version of its Little Big Disk series of Thunderbolt drives Promise had to respond.

The result is this, the Pegasus J2:

The design is extremely unique. While most Thunderbolt enclosures thus far have been home to either 2.5" or 3.5" drives, the Pegasus J2 houses two 6Gbps mSATA SSDs in RAID. I've already demonstrated the sort of performance you can get from RAIDing together two relatively cheap 6Gbps SSDs, and the current crop of mSATA drives can actually equal the performance of their larger 2.5" brethren, so the J2 design makes a lot of sense. The real killer is this: the Pegasus J2 can deliver performance similar to the Pegasus R6, and in many cases it'll outperform it. Here's a shot of the J2 on top of my personal R6 on my desk:

That's the beauty of solid state storage. That little box on top can outperform the big thing beneath it.

Capacity is a problem of course. Promise is only offering the Pegasus J2 in 256GB and 512GB capacities, while you can up to 35x that storage in a maxed out Pegasus R6. I'm less interested in the J2 from a practical standpoint for now, and more intrigued by the form factor and what it could mean for future external Thunderbolt storage. We have the technology now to hit 1TB inside the J2 chassis, and next year that number will grow to 2TB with the move to IMFT's 128Gbit 20nm NAND. The capacity problem goes away over time, but for now it's a definite concern.

Promise also isn't releasing any pricing information today, but rest assured that the Pegasus J2 will be expensive. In our My Book VelociRaptor Duo article I included a chart of the cost-per-GB of many currently available Thunderbolt enclosures:

LaCie uses Intel SSDs in its Little Big Disk at $2.917 per GB. It's possible that Promise can do better, we'll have to wait and see closer to official availability if it can however.

The Drive & Bundle

The J2 is subtly styled. Rather than being a rectangle there's a slight wedge taper in the middle of the profile. It sort of looks like my attempts to draw a sportscar in middle school, but better. Build quality and feel are top top notch, better than the Pegasus R-series for sure. The chassis has a solid but not heavy feel to it thanks to material choices. The top cover is a thick piece of aluminum, while the bottom of the chassis is finished in a soft touch plastic. Around back there's a single Thunderbolt port and an optional DC input. The J2 can be operated using bus power or pull from a supplied power adapter. You can switch modes on the fly, you simply get more performance when plugged into the wall. Remember the Thunderbolt spec only allows around 10W to be supplied over the cable itself. Take into account two 6Gbps SSDs (each of which likely draws between 3 - 5W under load), the internal SATA controller, and the power consumption of the Thunderbolt controller + active cable and you're easily beyond 10W. Promise has its own custom SSD and ASMedia SATA controller firmware that allows it to throttle performance when running on Thunderbolt bus power to keep below that 10W maximum. There's no reconfiguring or software changes needed when you switch between operating modes, just plug in the drive's external power and you get better performance. The bulk of the J2's power still comes from the Thunderbolt bus. With the external power adapter plugged in the J2 draws at most 1.1W from it at idle, and up to 2.9W under load - the rest comes over the Thunderbolt cable. A single LED indicator on the back of the drive lets you know what mode you're running in. Green for bus powered (low performance) and blue for external power (high performance):

The J2's optional power brick comes with a set of removable plugs for international use:

The Pegasus J2's bundle also comes with a carrying case. There's no Thunderbolt cable included unfortunately.

The chassis is super easy to get inside, there are three phillips head screws that keep the two pieces together. Two are beneath rubber feet, while the third is in the middle of the base of the chassis. Once removed you can slide the aluminum cover forward and pry the two pieces apart:

There's a small, notebook fan inside the aluminum cover to the J2 (if you are taking one of these things apart be careful when opening the J2 as the fan gets power from the underside of the PCB). The fan never gets too loud but it helps keep the tiny SSDs cool.

The PCB itself is a pretty neat looking design. There are two mSATA SSDs placed side by side:

Thermal pads cover the bottom half of the drives, the top half is cooled by the J2's fan. The drives use Phison's PS3108 6Gbps SATA SSD controller, typically used in entry level, value SSDs. Sequential performance is good, but random write speed isn't and in a heavily fragmented state performance can drop significantly. I suspect Promise chose the Phison solution because of the low cost, low power profile and the ability to modify firmware. The only problem is I'm not sure if I'd be too comfortable paying for a premium product using distinctly value SSD controllers.

SATA duties are handled by ASMedia's ASM1061 PCIe 2.0 x1 to 6Gbps SATA controller. Like most Thunderbolt enclosures that rely on a RAID array of drives, the Pegasus J2 uses software to handle all striping/mirroring duties. In the case of the J2 under OS X, you'll be using Apple's Disk Utility to switch between RAID-0 and RAID-1.

Thunderbolt support is provided by an Intel Port Ridge controller (the tiny IC labeled L2201). Port Ridge is a Thunderbolt end point controller, meaning it only has a single Thunderbolt input and can't pass PCIe/DP to any other devices down the chain - it terminates the Thunderbolt chain. Port Ridge is lower cost Thunderbolt controller often used for these types of tiny, bus powered devices. Since you can only have one bus powered device per Thunderbolt chain, it makes sense to use a controller that can only operate as an end point.



View All Comments

  • likethesky - Saturday, September 08, 2012 - link

    Why go TB, when USB 3.0 is just about as fast? Or am I wrong about that for SSDs? Reply
  • Zds - Sunday, September 09, 2012 - link

    USB 3.0 is 5Gbps, TB is 8Gbps - and this device uses all that on sequential reads, hitting 770MB/s. Reply
  • repoman27 - Tuesday, September 11, 2012 - link

    Well, SuperSpeed USB is 5 Gbps with 8b/10b encoding, so really only 4 Gbps, and realistically tops out at 400 MB/s due to protocol overhead. If you're using USB 3.0 drivers and/or hardware that only support standard Bulk Only Transfer mode, throughput will be considerably less than that.

    Thunderbolt is 2x 10.3125 Gbps channels per port with 64b/66b encoding which brings them down to 10 Gbps. While most Thunderbolt controllers have a PCIe 2.0 x4 back end, the Port Ridge controller used in this device only provides a single 10 Gbps Thunderbolt channel paired with a PCIe 2.0 x2 connection.

    A PCIe 2.0 lane is 5 Gbps but also uses 8b/10b and has its own protocol overhead, which in practice results in throughput of about 400 MB/s, although better results can be achieved with larger TLP payload sizes.

    So any Port Ridge based Thunderbolt device would be limited to around 800 MB/s, which is exactly what we see here.

    There's one more element to the equation though, and that's the SATA controller. Most USB 3.0 to SATA bridges on the market at the moment only support SATA 3Gb/s, which limits them to less than 300 MB/s (8b/10b strikes again). Meanwhile, most SATA 6Gb/s controllers used in Thunderbolt devices only have a PCIe 2.0 x1 connection which drags them down to 400 MB/s. Which makes me confused about the Pegasus J2's performance, because that's what we would expect from a single ASM1061 controller. I'm guessing there's a second one on that board somewhere.
  • Zds - Sunday, September 09, 2012 - link

    What are the dimensions of the device? It feels strange to applaud the small size, but not tell _how_ small exactly it is.. Reply

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