Promise Pegasus J4 review: An unconventional Thunderbolt storage device

Performance
Our review unit came with four Toshiba 500GB internal drives, model MQ01ABD050. These are regular laptop drives that spin at 5,400rpm. You can, however, use faster drives that spin at 7,200rpm, or even solid-state drives (SSDs). (See the compatibility list.)

I tested the J4 in all three configurations, RAID 0, RAID 1, and JBOD, and it offered good performance, considering it was using slow hard drives. As with all multiple-bay Thunderbolt storage devices, I did two sets of tests. The first, called Thunderbolt vs. Internal, has the least involvement of the test machine. In the second, Thunderbolt vs. External, I tested it by copying data back and forth from the test machine. The computer used for this test is a late-2011 MacBook Pro running Mac OS 10.7 and with a SATA 3 SSD.

Thunderbolt vs. internal
This is the test in which the reviewed Thunderbolt storage device shows its performance just by itself and when working with another Thunderbolt device. Internal drives are thrown into the mix because prior to Thunderbolt, internal drives were the fastest storage devices on the market.

In this test, the J4 excelled in RAID 0, scoring about 300MBps when copying data from another Thunderbolt drive. When it was set to copy data within itself, doing both reading and writing at the same time, it registered 92MBps, about the average.

It was quite different when the J4 was set up in RAID 1, however. Now it scored 103MBps when copying data from another Thunderbolt device and just 37MBps when copying data within itself.

Finally, in JBOD, the J4 registered 103MBps and 39MBps for the unit-to-unit and self-read and write tests, respectively.

Note that due to the nature of JBOD and RAID 1, the performance of the J4 in these two configurations was basically that of a single internal drive.

Data transfer, Thunderbolt vs. internal (in MBps)
(Longer bars indicate better performance)
Unit to unit  
Self-read and write  
Promise Pegasus R6 (RAID 5)
323.79 
192.53 
Promise Pegasus J4 (RAID 0)
299.9 
91.86 
Crucial m4 (internal drive)
235.51 
117.99 
LaCie Little Big Disk SSD
233.5 
141.69 
WD VelociRaptor 600GB
126.33 
58.05 
Elgato Thunderbolt SSD
121.96 
71.84 
Seagate Barracuda XT
115.71 
51.1 
Promise Pegasus J4 (RAID 1)
102.95 
36.88 
Promise Pegasus J4 (JBOD)
102.79 
38.6 
Drobo Mini
101.17 
45.16 

Thunderbolt vs. external
In this test the J4 was used with the test computer, which is how it's most likely to be used in the real world.

In RAID 0, the device again excelled, at 200MBps for writing and 156MBps for reading. In RAID 1 the score was reduced to 111MBps and 110MBps for writing and reading, respectively. Finally, in JBOD, it scored similarly at 111MBps and 95MBps for writing and reading.

Overall, the J4 performed very well for a Thunderbolt device of its type, and remained cool even during heavy loads.

Data transfer, Thunderbolt vs. external (in MBps)
(Longer bars indicate better performance)
Read  
Write  
Promise Pegasus R6 (RAID 5)
177.53 
210.5 
Promise Pegasus J4 (RAID 0)
156.26 
200.31 
Promise Pegasus R4 (RAID 5)
171.1 
150.47 
Promise Pegasus J4 (JBOD)
95.24 
111.17 
Promise Pegasus J4 (RAID 1)
109.77 
110.71 
Drobo Mini (via Thunderbolt)
94.66 
106.03 
Drobo Mini (via USB 3.0)
76.79 
59.26 

Conclusion
The four-bay Pegasus J4 is very much a combination of two dual-bay storage devices housed in one compact package. If you can overlook the current lack of RAID 5, you won't be disappointed by its performance and ease of use.

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Promise Pegasus J4 (2TB)

Part Number: J4HD2TBUS
MSRP: $399.00 Low Price: $942.00 See all prices