Send us a Topic or Tip

Have a suggestion for the blog? Perhaps a topic you'd like us to write about? If so, we'd love to hear from you! Fancy yourself a writer and have a tech tip, handy computer trick, or "how to" to share? Let us know what you'd like to contribute!

Thanks for reaching out!

Get Up to 67% Faster External Drive Performance With Your M1 Mac!


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…


The What

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:

The How

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.

Transparent Thunderbolt Logo

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.

The Why

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.

The Results

External Thunderbolt Drive Performance Improvement When Connecting a Thunderbolt Display to an M1 Mac

Our tests consisted of AJA System Test v15.5.3.1, 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.

OWC Envoy Pro FX (2TB)

  • Mac mini
    • 663MB/s better write performance
    • 1704MB/s with display vs. 1041MB/s without display
    • 63% speed increase 
  • MacBook Pro
    • 658MB/s better write performance
    • 1783MB/s with display vs. 1125MB/s without display
    • 58% speed increase
  • MacBook Air
    • 653MB/s better write performance
    • 1782MB/s with display vs. 1129MB/s without display
    • 57% speed increase

OWC Envoy Pro EX (4TB)

  • Mac mini
    • 660MB/s better write
    • 1691MB/s with display vs 1031MB/s without display
    • 64% speed increase
  • MacBook Pro
    • 723MB/s better write
    • 1787MB/s with display vs 1064MB/s without display
    • 67% speed increase
  • MacBook Air
    • 669MB/s better write
    • 1768MB/s with display vs 1099MB/s without display
    • 60% speed increase

USB-C Envoy (960GB) 

  • Mac mini
    • 101MB/s better write
    • 729MB/s with display vs 628MB/s without display
    • 16% speed increase
  • MacBook Pro
    • 143MB/s better write
    • 721MB/s with display vs 578MB/s without display 
    • 24% speed increase
  • MacBook Air
    • 141MB/s better write
    • 720MB/s with display vs 579MB/s without display 
    • 24% speed increase

Example Speed Test

To give you a visual, we asked Brady to run another sample test and send us some screenshots. This is what he sent over:

The sample tests below were run using a Thunderbolt 3 OWC Envoy Pro EX (with a 2TB Aura P12) connected to an 8-core M1 MacBook Air with 16GB RAM. They were run with and without a Samsung F32TU872VN monitor (connected via its included Thunderbolt 3 cable), AJA version, and Black Magic version 3.3.

AJA Speed Test - read and write speeds on an M1 Mac
BlackMagic DST Speed Test - read and write speeds on an M1 Mac

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!

OWC Grant
the authorOWC Grant
Grant is OWC’s Brand Evangelist and works closely with OWC’s product management and development teams to laser focus on what OWC branded products can offer to a wide variety of technology users. Grant helped launch numerous OWC and NewerTech innovations from 2005-2012 and rejoined the team in 2019 to passionately tell our brand story.
Be Sociable, Share This Post!

Leave a Reply




  • I’d be happy to get an externally connected SSD to work via the USB-C/Tb port at all!
    Tried two enclosures, with same result. They work fine when connected by USB-A (although very slow) but won’t even show in Finder when connected by USB-C.
    Both enclosures work as expected on 2017 iMac using USB-C/TB

  • Busy weekend. Couple things. 1) headless emulator requires HDMI port, with the MBA/MBP don’t have requiring a hub. I already bought the OWC TB3 mini hub because my OWC Envoy Express and Fledging Shell Thunder couldn’t be connected to the two TB ports on the MBA at the same time–not enough power? 2) DEMinSoCal talks about getting nice R/W speeds using BlackMagic. Please set to 5GB and see what you get. BM is for validating video files and can skew some results, especially with SSDs with a lot of cache. 3) DEMinSoCal again, what SSD enclosure are you using? The OWC Envoy Express (with same Phison blade as Fledging) is a x2 channel interface while the Fledging is a x4 channel, which makes a lot of difference. 4) Not sure I mentioned this but I get the same Write speed on these drives when connected to my TB2 iMac using Apple’s TB2-TB3 adaptor, only the Read speed is slower. 5) For those who are wondering about which SSD enclosure to get, I’ve asked several times (OWC responded several times) about having OWC list advanced technical specifications for their Thunderbolt external drives so we can see which ones use single channel and which ones use multiple channels plus whether they’re PCIe 3 or 4 (OWC Express 4M2 but with four blades RAID’d its very fast–Grant, might want to try it and see if the number of channels have anything to do with it, OWC Envoy Express two channels, Fledging 4 channels). Enough for a Monday morning.

  • 2243 MB/s write and 2827 MB/s read (using BlackMagic) on my TB3 SSD and M1 Mac Mini and I don’t have a Thunderbolt display. I think it’s more about the external SSD enclosure than this idea of needing a Thunderbolt display.

  • Fascinating discovery. Now if Apple can only find a way to tell the Mac to disable video support on TB4 so that the bandwidth is not held in reserve, or more intelligently let full bandwidth be used if no display is connected to that port. Either way, findings are definitely worth reporting to Apple! Good work!

  • Here’s my theory.

    Thunderbolt video requires a different bandwidth allocation than a Thunderbolt drive because it is a one-way flow (“writing” to the display but not “reading from it). When connecting such a display, the controller is told to allocate more bandwidth in one direction out of the Mac and into the display. If both Thunderbolt ports are connected to the same controller, this has the simultaneous effect of widening the write bandwidth of the other port, increasing the data-flow to that drive, resulting in better write performance. This higher data-output flow mode is likely only turned on when a display is connected to save energy consumption and heat output. Maybe a customer shouldn’t think of his performance being degraded unless he plugs in a Thunderbolt display, he should think of getting a free undocumented boost of performance when connecting one. Perhaps this should be configurable as a setting in the Energy preference pane.

  • I have M1 Mac Mini, 2 OWC Thunderbolt hubs, a LG Ultra fine display and an Envoy Pro Ex 2TB external drive. I have the Thunderbolt Display and one hub hooked up to the Mini. The other hub and the external drive are hooked up to the first hub.

    Is that the best I should do?

    • Hi Paul and thanks for your interest in this topic. I haven’t written it up yet as I need to confirm a few things…BUT….looks like IF you have a TB hub or dock, you can plug your monitor into that, plug your hub or dock into M1 Mac, AND have your external drive connected DIRECTLY to the other M1 Mac TB port, you will see the same speed increase on your external drive.

  • This is really good to know! My iMac is “ancient”, sporting “only” Thunderbolt 2 ports, so I there’s no impact for me and the only somewhat heavy duty work I do is photo editing of high resolution files and scans. But it’s good to know for the future if I feel the need to upgrade.

  • What about running a M1 headless?

    No displays connected. Just using Screen share or VNC to control mac.

  • Is it possible to configure Blackmagic Disk Speed Test to show the maximum or average read and write speeds to take screen captures? I ask because it loops again and again and it is difficult if not impossible to take a screen capture of such maximum or average seed.

  • I won’t be able to experience “Performance Improvement When Connecting a Thunderbolt Display to an M1 Mac ” until Apple delivers my Thunderbird 3 to Thunderbird 2 adaptor.
    As I thought about possible ways to get this new M1 Mini working RIGHT NOW I thought of the 30″ Cinema Display and its fancy adaptor sitting in the closet. Any reason why this (and its 23″ little brother) would not work with an M1 Mini? Which dock or hub would be most likely to work? The Akitio seems like a nice piece, perhaps I could have both the Thunderbird display AND the 30″ Cinema display, which would make my wife crazy……

  • Hi joevt. I tested the Feldging enclosure with Phison blade both directly connected and connected through OWC’s new 4-port TB hub. I got similar R/W results. I did notice something confusing when checking System Report/Thunderbolt-USB4. It reported the 4-port hub with a Link Width of 0x2. Does this mean the hub is limited to only two channels instead of four which I thought the Fledging has in its controller? Again, this is why I am hoping MacSales/OWC will start including PCIe channel width in all their external disk and hub specifications. To most people, me included, it will be TMI but it could also help identify and understand what might be going on and where potential bottlenecks are. Running Amorphous on a directly connected Fledging drive I still only got R/W first results of 2525/981 so it is only reporting slightly faster Read speeds than AJA. Blackmagic is the one that shows the highest Write speeds of 1646 with Reads in the 2400 range. (Drive connected to TB0 port)

  • This sounds like a serious flaw in the design/operation of the M1 Macs. I have the M1 Mac Mini. Purchasing a thousand dollar monitor/display to correct Apple’s mistake is a non-starter.
    Hopefully it can be corrected with firmware. If not, I think Apple should recall and repair all flawed machines.
    Shame on Apple for its lack of transparency regarding this issue. And others.

    • Absolutely well said Not good enough Apple! This should’ve already been fixed.

      The comment I was gunna make was does OWC have a contact at Apple that they relay their findings to? I realise they still might not do anything but hopefully it puts more pressure on them to come up with a fix.

  • Do you know if this is a feature or a bug? Is there any way you can pose this “feature” to Apple and see what they say? It really makes your hardware look slow and/or makes Apple look bad when pushing their own SoC. Of course I could always submit a Support call and reference your experience and ask Apple what’s going on. I tested the same TB3 drive on my late 2015 iMac (TB2 to TB/TB3 adaptor to ThunderBay RAID to external drive) and it got 950+ on write. Kind of makes my old Intel iMac look better than my brand new M1 MBA. ;-)

  • The explanation for why this happens is interesting but the logic seems broken even for Apple.

    I think I’ve read in various places of people connecting a fake second display to a GPU to improve performance of the real display. Like, with one display, the hardware is in a lower power mode (lower GPU clock?). Maybe that’s what’s happening with the M1: not connecting a display puts the hardware in a lower power mode, reducing performance?

    Is there performance info in the IO registry that gives a clue? Is there a utility like Hardware Monitor for the M1 Mac? There’s iStat Menus and Sensei but I don’t think they’ll show a difference with these different M1 tests?

    I look forward to your future tests (display connected directly, display connected to USB-C non-Thunderbolt dock, … etc.)

    • Hi joevt and thanks for all your input and questions. We definitely have more investigation and testing to do, but we at least wanted to get the big insight out first as so many users have noted slow external drive speeds in reviews and videos. Keep watching the blog for updates!


      Joevt…I discussed your thoughts with other team members about how the GPU could be accelerated for better system performance.

      Per GeekBench5, system performance for an M1 MBA10,1 is relatively unchanged by the addition of a Thunderbolt monitor. In fact, it performed slightly worse with the monitor attached (7716 multicore score with no monitor vs 7687 with a TB3 monitor)

      Additionally, Cinebench R23 saw similar benchmarking with an M1 MBP17,1 seeing a score of 7800 without an additional monitor, and 7789 with a Thunderbolt monitor.

      What it truly comes down to -at least to us – is that port specific I/O performance is affected by the addition of the Thunderbolt monitor. The port the monitor is plugged into sees no increase in write speed, it’s only the port without the monitor that sees/delivers the speed increase.

  • A Thunderbolt display internally is just a DisplayPort display connected to a Thunderbolt dock so you should get similar performance increases with that setup.

    The Thunderbolt write speeds are still low. Maybe try with something like a Sabrent 2TB Rocket Nvme PCIe 4.0 (it’s overkill since Thunderbolt 3 is PCIe 3.0 but it removes NVMe write speed bottleneck). Also, AmorphousDiskMark.app gives higher benchmark numbers (it’s not real-world, but it gets closer to the theoretical max of the interface).

    Your tests include USB 3.1 gen 2. Most NVMe in a USB enclosure (including lower performance Intel 660p) should be able to get 1050 MB/s but the M1 Macs have lower performance USB (even for USB 3.0 devices). Connecting a USB drive to a Thunderbolt 3 dock should improve performance because the Thunderbolt 3 dock has its own USB controller that is superior to the one in the M1 Macs (even though you have to deal with Thunderbolt latency).

    Some Thunderbolt 3 docks have multiple USB controllers. Be sure that you’re using the Thunderbolt controller’s USB controller (connect your USB device to the downstream Thunderbolt port) because it’s superior to most other USB controllers used in Thunderbolt docks. A Titan Ridge based Thunderbolt 3 dock will have another USB port connected to the Titan Ridge Thunderbolt controller’s USB controller. A Titan Ridge Thunderbolt 3 dock usually won’t include other controllers because they can’t work with Titan Ridge’s ability to connect to non-Thunderbolt hosts (this also applies to Thunderbolt 4 devices since they can also be connected to non-Thunderbolt hosts).

    Other USB controllers in a Thunderbolt 3 dock (usually Alpine Ridge based) may include the ASMedia ASM1142 which is limited to PCIe 3.0 x1 or PCie 2.0 x2 (7.877 Gbps or 8 Gbps – worse than M1 Mac) and the Fresco Logic FL1100 (a USB 3.0 controller limited by PCIe 2.0 x1 – 4 Gbps (USB 3.0 is also 4 Gbps but PCIe 2.0 has more overhead?). The FL1100 has less performance than USB 3.0 connected to the ASM1142 but probably better than USB 3.0 connected to M1.

    However, a Thunderbolt 4 Hub or Dock may use USB tunnelling (a new feature of USB4 and Thunderbolt 4) which connects the USB drive to the USB controller of the M1 Mac so you don’t get the benefit of the USB controller of the Thunderbolt controller of the Dock. In that case, you need to check the USB tab in System Information.app to see what USB controller (USB Bus) the USB drive is connected to. Did earlier versions of Big Sur not use USB tunnelling so that the USB controller of the Thunderbolt 4 hub/dock could be used? I’m not sure if I’ve seen that tested – I’ve seen one person show USB tunnelling working in the latest version of Big Sur with a OWC Thunderbolt 4 Dock. Does the OWC Thunderbolt Hub also do USB tunnelling (I thought I read somewhere that it improves performance because its USB controller is being used but I may be mistaken)?

    • Interesting comment as I’m interested in a lot of the actual nitty gritty of how it all works and also saw that there’s been thunderbolt docks released that can ‘fallback’ to USB but I thought surely there’s a compromise with those in how they work no to enable this fallback?

      The USB tunnelling also sounds very interesting!

  • To put it bluntly, great job of finding the answer but at the same time this sucks big time and I bet every M1 Mac user agrees with me.

    Let’s step back and see what’s going on. I guess a chart would help myself and others. I have a TB3 external disk (actually two, OWC PCIe x2 and Fledging PCIe x4–same Phison NVMe blade (OWC rebranded this for their Aura blades, both 1TB).

    I can’t plug both drives into my MBA and get both to work. The only way is to use a hub (OWC 4-port TB hub in my case, it’s powered). This also upsets me but I was getting the hub anyway.

    The M1 only supports two TB ports but the PCIe bus is shared between the video xxx (what? not GPU) and TB ports, reducing the write speed to the TB ports significantly.

    If I buy a TB display, what happens to the MBA display? Does it turn off? If not, why is the write speed of external drives increased if the display is still on along with a second display also using ????

    The fact you got it to work is great but none of this really makes sense because the external display is being sent video through the TB port which should be slowing down the write speed as well.

    Totally confused and not happy that I’d need to spend money on a TB display (well, I was thinking about getting one for the MBA then retiring my Intel iMac but that doesn’t count) just to get proper write speeds.

    • Hi Peter and thanks for the reply. The external display is being handled by one of the M1 Mac’s Thunderbolt ports. This then – we are suspecting – has the M1 chip telling the other Thunderbolt port “hey…you don’t have to worry about video signal, so you can go full data bandwidth speed if an external drive is connected to you.” I try to humanize tech sometimes so it’s more approachable. Hope that explanation helps! And hold on on spending any $$$ on a TB display. We have lots more testing to do with Thunderbolt and USB-C hubs, docks, etc. One never knows what we’ll find!

      • So on this, does this mean that the default nature of the thunderbolt ports is to ‘reserve’ outbound bandwidth for DisplayPort data but then as ya say, once one port supplies this and due to the limitation of 1x external display (an absolute shambles this fact alone Apple!), then it knows that it doesn’t have to hold this reserve for DisplayPort and by switching into some sort of ‘full PCIe mode’, it then enables faster outbound/write data speeds?

        Also why the specific thunderbolt port? It shouldn’t matter if designed correctly right? Just bizarre stuff ‍♂️

        • Hi Lahmy and your summary is pretty spot on. Still not sure if it’s the M1 chip and TB ports communicating to one another and creating this scenario, but bottom line is something is “telling” the other TB port on host Mac, “hey, the other TB port is handling video so you got full bandwidth for data if you have an external drive connected to you”

          I try to humanize tech sometimes so its just more down to earth. Hope that helps. Should have some new insights on this topic this week.