If you are thinking of buying a M1 powered Mac and rely on fast, external, storage via a USB-C interface, you may want to reconsider.

The Thunderbolt/USB-C ports on M1 Macs don’t work. They work to some degree, they just don’t work properly; they don’t allow attachment of many external USB-C enclosures. The same devices that do work when attached by a standard USB-A connector. And do work with either connector when attached to an Intel based Mac.

Things tried so far, including talking to Apple support

The cynics among you may assume I have not been thorough in my troubleshooting.

Here are the steps taken so far.

  • A Silicon Power 2TB SSD NVMe M.2 in a SHE-C325 enclosure attached to 2017 iMac 27″ works perfectly whether attached by TB/USB-C or USB-A
  • Attached to Mac Mini M1 it initially showed in Finder/Disk Utility, but after about 2 minutes ejected itself never to be seen again
  • After the initial moment of showing, the same disk on a Mac Mini M1 now can’t be seen in disk utility with either USB-C/TB port
  • Reboot? Same issue
  • Start in Safe Mode (Apple Supports insistence) – Same
  • Create a new admin user (Apple Supports insistence) – Same
  • Try re-partition of the drive as APFS – Same
  • Try re-partition of the drive as Mac OS Extended – Same
  • Same hardware back in iMac (Intel based) – works fine

Maybe it is some compatibility with the controller on the SSD enclosure? I ordered a new enclosure; a Sabrent USB-C M.2 PCIe NVMe.

Different hardware, same result. I have tried this on every released version of Big Sur, including the latest 11.3 at the time of writing (using Big Sur on the iMac too, so nothing to do with disparity in OS versions).

Tried all the same steps with the brand new enclosure and got the same result.

More examples of the issues

Now it is possible that both these enclosures use the same micro-controller – I don’t know if there is an easy way to work that out? But I can tell you that my scenario is far from isolated. None of the Mac focused reporting sites seem to have picked this up. Well, they have regarding monitors via USB-C, but not other devices: https://www.macrumors.com/2021/02/03/macos-big-sur-external-display-issues/

However, from a quick search about issues with the TB/USB-C ports on Mac M1 machines you turn up plenty of similar complaints:

What does work

Two things it seems. One I can tell you from experience does work, and one from reading the reports of others online.

Connect it by USB-A and take the speed hit

Until Apple sort this, and I am perhaps being optimistic they will, one thing I can tell you with complete confidence does work is connecting the same external enclosures by the USB-A port instead. Now, this is far from perfect as you are then taking a huge hit in performance, which is what you likely ended up buying this level of SSD kit for in the first place. But…

That will at least allow you to access the drive, get files, or just use it as a backup device with Time Machine.

Connect via a Thunderbolt Hub

Threads on Mac Rumors suggest the same devices connected via a Thunderbolt dock, such as the CalDigit TS3+ work fine. However I’m not about to spend another pile of cash to get something as simple as a USB drive working!


There is something ‘not right’ with the USB-C/Thunderbolt ports on the M1 powered Mac’s – it feels like there is some yet unresolved hardware/driver issue.

If you have had similar issues, let me know in the comments, or better still, get on to Apple support and raise a case. Sadly, I think that’s the only option of getting anything to the Apple mothership. In classic Apple style, we users know nothing of whether this issue is known at Apple, and, if known, whether it is actually being worked on, impossible to sort or can be sorted but not for some time.

Should anything come of my continued support case with Apple I’ll update here.

Update 12.5.21

The plot thickens!!!

If I stop using USB-C to drive my display, leaving both TB/USB-C ports free, then plug this drive into one of the ports, the drive connects and operates as expected.

There is obviously something that these two ports can’t do at once, in this case, drive a display and a USB-C drive at once.

So, that’s pretty bad. Good I can see the drive working as it should using USB-C but now I have a different issue. Driving my display (BenQ 3200u) with HDMI doesn’t give me the same range of display scaling options I get with USB-C. It goes from 2560×1440 to 3840×2160; misses out the 3072×1728 area option I use. Suspect that is because via USB-C there is enough bandwidth to double the 3072×1728 and then scale it down to fit in the 4K, where HDMI 2.0 has a max resolution of 3840×2160

Beginning to think these M1 machines aren’t all they are cracked up to be! This feels like related issue to the one that Rocket Yard reported days ago.