Not getting the write speeds you were expecting with an external drive on your M1 Mac? You’re not alone. Read on, because we found something interesting…
Testing products is a way of life here at OWC and has been nearly from day one. Our product development team is constantly taking a deeper look at Apple products—and our own—to see if we can uncover some hidden potential to help you get more from your technology investment. From performance benchmarking to inform you of your “best-bang-for-the-buck” OWC upgrade to determining which Macs can have double the amount of RAM than what the factory supports, you can count on OWC to be your trusted source for key insights.
It’s been widely covered in posts and videos how external drive performance is unacceptably slow with the M1 Macs. Well, we have some breaking news on this subject and you’re reading it here first on the Rocketyard Blog:
One of our product dev team members, Brady Campbell, came across this while running some tests between two M1 Mac minis. When connected to a 2TB OWC Envoy Pro EX, Brady found one of the minis wrote to the Envoy Pro EX at much higher speeds. As both minis should write to the same external drive at the same speed, Brady began investigating what could cause this anomaly.
Through the process of elimination, the only variable was that one of the minis was connected to a Thunderbolt 3-equipped display while the other mini was connected to a non-Thunderbolt display via HDMI. When Brady switched the displays, the faster speeds followed the Thunderbolt display.
To double-confirm having a Thunderbolt display attached to an M1 Mac mini creates this speed boost, Brady performed the same test with another Thunderbolt 3-equipped display and found the same increase. Subsequent testing on an M1 MacBook Pro and MacBook Air revealed the same speed increase.
Our theory to what causes this dramatic speed increase is that the M1 CPU only supports one video output signal to its TB4 ports. When a Thunderbolt display is connected to an M1 Mac’s TB4 port, the other Thunderbolt 4 port on the Mac does not need to support video output. It can then deliver the full PCIe data bandwidth potential to an attached external drive. Inquiring minds might ask, “why aren’t the read speeds affected?”
Simply put, Thunderbolt technology doesn’t use bandwidth for an input (read) video stream.
External Thunderbolt Drive Performance Improvement When Connecting a Thunderbolt Display to an M1 Mac
Our tests consisted of AJA System Test v220.127.116.11, and all results were verified in Black Magic v3.3. The M1 Macs were running Big Sur 11.3 and were connected to either an LG 32UL950-W or a Samsung F32TU872VN display – with speed results being consistent for each display.
The Next Step
So, where do we (and you) go from here? We’re going to be hard at work testing what effect other drives, docks, and adapters – including USB-C versions – have on this external drive/external display scenario. We’re even going to check if our HDMI Headless 4K Display Emulator can “trick” an M1 system into thinking an external display is connected!
So, keep reading the blog to learn which OWC solutions you own – or should consider adding to your setup – have been test-verified to deliver this speed boost!