Promise J2 full review

Promise Technology is a Taiwan-based company specialising in professional storage products. We rarely see its products at the consumer level, although in 2011 Promise drew the limelight as the first company to launch a Thunderbolt product, outside of its creators Intel and Apple.

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The Promise Pegasus R6 was a mighty six-bay desktop RAID box exploiting the new high-speed interface. Fast, very; and highly capacious with 12TB of online storage.

Now at the other end of the scale – in size terms anyway – is the Pegasus J2.

The Pegasus J2 is Thunderbolt drive based on solid-state flash storage. It’s actually built around two mSATA modules, configured by default in a RAID 0 striped array for best performance. RAID is achieved in software in OS X. It’s available in either 256 GB or 512 GB capacities.

Only 110mm long, the Promise J2 is truly pocketable, even with its strangely stepped profile, about 18mm thick one end and 21mm the other. That’s to accomodate an internal fan which kicks in when the device is working at peak performance.

And what a peak that can be too. While the company’s own Pegasus R6 just beat it in simple sequential read speeds, the J2 has a major advantage in random read/write speeds, as you might expect from an SSD compared to spinning platter technology.

Promise J2: Build and bus

Build quality is satisfactory, if a little uninspired. The top of the drive is crafted from matt-finish natural aluminium; the underside a rubber-finish black plastic. The overall effect is not quite what we'd expect of nigh-on £400-worth of tech. It also leaves the unit strangely top heavy in the hands. You do get a premium feeling real leather pouch for it, with elasticated sides and magnetic clasp.

The Promise J2 can be operated from just Thunderbolt bus power, or with the aid of a small mains adaptor. By supplementing the limited current provided from the bus, the J2 is able to work at its full rated speed. When you don’t have access to mains electricity it will still work, only at a reduced speed.

It does this by cleverly leveraging one feature of storage that might be more readily accessible than the rest – the cache. So when extra electrical power is available, the RAIDed SSDs are used as normal with the full benefit of onboard cache; on bus power the cache is disabled. This may only save a little power, but enough to allow two SATA 6Gbps drives to operate from Thunderbolt’s limited 10W power budget.

Promise J2: Performance

Out of the box, and powered only from the Thunderbolt bus of our MacBook Pro (Mid 2012), the Promise J2 proved to be about the equal of the Elgato Thunderbolt SSD – in read speeds anyway – cruising along at around 267 MBps for large sequential reads. Elgato’s bus-powered drive recorded 270 MBps in the same QuickBench test, with disk cache effects disabled.

The Promise J2 read speeds rose to 342 MBps with the benchmark’s ‘disk cache effect’ setting enabled, which we found odd given that there was not supposed to be any cache available. Promise Technologies’ engineers would not reveal details about the size or nature of cache in this device, although the concept of automatically switching depending on power source does seem notably innovative.

Write speeds on bus power were already ahead of the Elgato, though, at around 310 MBps. For 4kB random read/write performance, the Promise J2 achieved 15 and 28 MBps; in the mixed file-size test, using data from 4kB to 1024kB, the drive averaged 91 and 134 MBps respectively.

Promise J2: Turning up the power

So the Pegasus J2 has usefully swift performance in a field setting. But what happens when the drive gets some extra adaptor power? The headline figures here were quite remarkable – 783 MBps for large (20-100 MB) data reads, and a startlingly close 729 MBps in sequential writes.

At the small file size, QuickBench unusually reported random writes ahead of random reads. For example, 4kB peformance was 26 and 38 MBps for reads and writes. By the time we hit 1024kB data, the Promise J2 was already approaching top speed, with 568/622 MBps read/write.

The top-top speed may be just below a six-disk RAID from Promise Technology’s own desktop Pegasus R6, but small file transfer characteristics were faster, small random writes around 50% quicker, for example.

Long-term performance is harder to gauge, with Promise using less popular SSD controller chip technology, a Phison PS3108. Garbage collection and wear-levelling strategies, crucial for long-term stability and performance are also unknown.

In use the unit did get a little warm, when used hard on adaptor power, usually followed by the faint whirr of the internal fan to keep temperatures down.

Regarding the style and design decision, we would rather see a slightly larger packaged unit with passive cooling, such as with a healthy heatsink.

Besides screaming performance the benefits of solid-state storage are silent operation and zero moving parts. As soon as you take the low-cost fan option, as well as spoil the peace it will demand cleaning and maintenance in due course.


Promise J2: Specs

  • Portable Thunderbolt storage drive
  • 256 GB total capacity (also 512 GB)
  • 2x Phison 128 GB mSATA SSDs
  • 1x Thunderbolt port
  • 12V DC inlet
  • external 12V/1A mains adaptor
  • leather carry case
  • 110 x 74 x 17.5-20.5 mm
  • 145 g (183 g with case)

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