Transcend JetDrive 855 SSD is an external storage drive that combines a PCIe JetDrive 850 SSD and an aluminum enclosure with cable and Thunderbolt connector.
The solution is suitable for all macOS users who want a capable unit, very fast (really a lot as we will see), silent and always ready to use.
The drive is designed for all Macs with Thunderbolt 1 and 2, but with a small adapter it is ready for even the most recent models with Thunderbolt 3.
Transcend JetDrive 855 SSD, how it's made
The unit arrives ready-made in a box with, inside, the Transcend JetDrive 855 SSD with the connection cable and, just below, a small instruction manual and two screwdrivers that are used to disassemble the case in case of SSD change.
The dimensions are very small: only 120 × 31.5 × 18.2 mm and a weight of 88 g on an external surface in satin aluminum (and a black rubber cable).
The speed test shows very high values and probably at the limit of the Thunderbolt connection
The Thunderbolt connection at 10 Gb / s is here pushed to the maximum: this connector is not (as we think) specifically designed for Mac but its diffusion in Windows has not been very lucky. However, there is no shortage of adapters to bring the drive to a new MacBook Pro, iMac or Mac mini with Thunderbolt 3 such as Apple's Thunderbolt 3 (USB-C) to Thunderbolt 2 adapter.
It is on a new Mac mini 2018 that we tested it and put it to the test.
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Disassembling the drive is not difficult and within everyone's reach, so when it's time to change SSD drives it can be done in a minute 
NVMe, the future is now
Inside the device there is a 3D NAND flash SSD drive on NVMe PCIe Gen3 x4 Bus, which offers incredible speeds: on paper the manufacturer indicates read values up to 1,600 MB / s and up to 1,400 MB / s in writing, even if in our tests we reached about half, still very good values and superior to any traditional SSD on SATA currently on the market, whose values are around 500 MB / s.
Disk management is also aided by the JetDriveToolbox App (for macOS and Windows) which gathers all the administration functions of both the internal SSD and the Thunderbolt case.
Technologies such as 3D NAND and the NVMe PCIe Bus are becoming increasingly popular, initially only in the gaming field but now also with a view to performance also suitable for the professional environment.
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The Disk Checker App 
How does it work
To test the disk, in our case of 960 GB, we copied the entire photographic archive, vector files and images, these divided between files in Jpeg, PSD and RAW.
This archive has always offered enormous problems of use because some folders contain more than 1600 PSD files with different levels and advanced objects that, typically, the Finder struggles a lot to render: Transcend JetDrive 855 SSD did not eliminate the problems, but it made the operation more human and user-friendly.
For all other archives, with for example Jpeg images, vector files, epub documents or other (just to mention the more complex formats) no problem, real time is really real time.
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Conclusions
While the Transcend JetDrive 855 SSD is designed for Macs with Thunderbolt 1 or 2, with a simple adapter it becomes one of the fastest and most capable portable drives on the market.
Quiet, heat-proof (even in the very hot August in Milan) and always ready for use, Transcend JetDrive 855 SSD has proved to be a faithful companion especially from a professional point of view to which, we admit, we will struggle to break away.
Furthermore, the possibility of changing the indoor unit with a new unit in a few years, perhaps more capacious, improves an already very good judgment for a unit whose compromises just do not exist.
Pro:
• Small and quiet • Lightning fast • Drive opens easily for changing SSDs
Cons:
• New Mac requires adapter
Price:
• 190.00 Euro (240GB) • 250.63 Euro (480GB) • 375.86 Euro (960GB)
Transcend JetDrive 855 SSD is distributed in Italy by Esprinet and Ingram so readers could find it in all Apple Premium Resellers in the peninsula, or directly from the Amazon pages.