I had a Sandisk Extreme Pro 500Gb PCIe NVME M.2 SSD. I got an USB-C 3.1 Gen 2 Enclosure for it. I have tried it on 3 different 2017 and 2018 macbook pros and an iMac. The Max read/write speed that I can get is 40MBps. I thought the problem might be with the enclosure so I tried 4 different enclosures and still same result. I installed the SSD through PCIe to a desktop and read/write speed were astonishingly high.

I got a Samsung T5 External SSD and even with one I have the same problem. I have seen many reviews of T5 on youtube with Mac which all were satisfied. Am I missing something? Do I need some sort of Driver for it? I’m running a 2018 Macbook Pro with MacOS Mojave

  • How exactly are you measuring those 40 Mbps? - I sounds like you're mixing up MB/s (megabytes per second) and Mbps (megabits per second).
    – jksoegaard
    Commented Mar 15, 2019 at 22:19
  • If he's using the wrong cable, a 40MB/sec peak transfer is very plausible. That's precisely what I get with my T3 and the wrong cable. Commented May 10, 2019 at 17:53

3 Answers 3


I own multiple Samsung T3's and T5's. They are incredible.

The cable is important, and unfortunately, it's impossible to tell which cables are intended for which purposes.

Your 2018 MacBook Pro with Mojave (I have a 2017) does NOT need any kind of driver to use the drive. There's an encryption app on the drive that's worth installing so that you can secure the contents, but that's orthogonal to speed.

Be sure you're using the short cable with the velcro bits when connecting to your T3/T5. For some of my Samsung T3/T5's, the old-style USB-A connector cable is the best one for performance.

Download the (I think still free) Blackmagic Speed Test from the Mac App Store and check the actual performance. Then change cables and you'll see what I mean.

As a rule, if the cable is more than 6 inches long, it's NOT for best performance. If the cable has the Thunderbolt symbol on it, it MAY be for performance, regardless of whether it has a USB-A or USB-C connector on the business end (toward your Mac). Also, DO NOT connect your T3/T5 through any kind of cable extender or dock. There's a distance limitation that you will run into if there's any kind of middle man device.

Before you down-vote me, please do what I've suggested. I literally have a dozen of these things, each 2 TB/$500.


Had the same problem just now with a Samsung 970 EVO Plus. Was using a 2 ft USB-C cable, and only getting 40 MB/s. Swapped out with a shorter cable and getting over 1000 MB/s. I should be seeing higher numbers though, so I'm going to purchase the highest quality cable I can find. Definitely the cable in this instance.

EDIT - It also seems the cable must be rated for USB-C 3.1 Gen 2... otherwise it doesn't matter what length you have.


Problem was quality of the cables. the cables were using the USB-C connector, but as you may know not all USB-C cables are equal. most of them are only intended for charging at low speeds and are not suitable for hight speed data transfer because they don't fully support USB-C specifications. They only use the connector. ( most probably with less wires inside the cable than required. not all pins are connected )

  • This is surprisingly common I believe. It may not be a guarantee and I'm sure there are exceptions, but the best way to confirm you are getting a quality cable in my experience is by reviewing its thickness. Better quality cables of the type required for these high speeds are normally better shielded and therefore thicker.
    – AdamJones
    Commented Jun 3, 2022 at 19:06

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