On the inside, the J2 comes with two micro solid-state drives (SSD), which explains how it manages to remain very compact. It would be much larger physically if it used two standard SSDs. While the compact design is welcome, the downside is that you won't be able to replace the J2's internal storage yourself, which slightly defeats the purpose of RAID 1, in case you want to use the drive in this data-safety-first configuration.
I reviewed the 256 version of the J2, and out of the box it's configured in RAID 0 to offer the best performance, and the full 256GB of storage space. The drive is preformatted in HFS+ for Mac; all you need to do is plug it in with a Thunderbolt cable of your own and you're ready to go. If you want to use it in RAID 1, which reduces its capacity to 128GB to offer redundancy for data safety, you'll need to use the Mac's built-in Disk Utility to configure and reformat it. This process took just a few seconds in my trials and will erase all existing data on the drive.
The J2 comes with no software and it can also be reformatted to use with Thunderbolt-enabled Windows computers.
The Pegasus J2 offered stellar performance when used with the included external power adapter. When used as a bus-powered drive, however, its performance took a big hit. And obviously, the drive is faster in RAID 0 then when used in RAID 1. Overall, however, no matter how you use it, it's still one of the fastest portable drives on the market.
I tested the drive thoroughly. First I used it with the power adapter, and in RAID 0 it offered 202MBps for writing and 181MBps for reading; both were about the top speed compared with its peers. In RAID 1, these numbers were lowered to 180MBps and 178MBps for writing and reading, respectively, which is still very fast.
When used as a bus-powered drive, however, its performance changed rather dramatically. In RAID 0, it now scored 84MBps for writing, about that of a USB 3.0 drive, and 153MBps for reading. In RAID 1, the writing speed was significantly lowered to just 31MBps, about the speed of a USB 2.0 drive; the reading speed, however, was still at 151MBps.
Overall, the J2 offered very good performance. I do wish, however, that it could offer its optimal performance even when used as a bus-powered drive. For now, you do need to choose between performance and portability. I did notice that the drive became rather hot in an extended operation, noticeably hotter than any other drive of the same type. While it wasn't hot enough to cause any problems and it worked perfectly throughout my testing, it did give me a little concern about the drive's rather short two-year warranty.
(Longer bars indicate better performance)
Supercompact, fast, and supporting RAIDs, the Pegasus J2 makes a very good investment for Thunderbolt-enabled Mac owners who can afford it. The fact that it lacks USB 3.0, requires the power adapter for top performance, and is pricey will likely steer many general users away.