investigation into disappointing Thunderbolt 4 speeds

investigation into disappointing Thunderbolt 4 speeds

A few days ago, specialists from The Eclectic Light Company blog highlighted the poor performance of the Thunderbolt 4 port on Apple silicon Macs for USB-C 3.1 Gen2 devices.

If we were unable to take measurements ourselves, not having the necessary equipment, we were able to count on the work of Atelier 440, a Parisian music school equipped with Mac mini and in particular Mac mini M1. We had access to data from their recent analysis made with several Mac mini, M1, Intel 2018 and Intel 20012, and two external hard drives, a Samsung T7 (USB) and one Samsung X5 (Thunderbolt). And the results shown by this new survey are hardly encouraging. They indeed confirm what we feared.

Samsung T7 External Drive (USB to Thunderbolt 3/4)

the Samsung T7 is an external SSD, NVME, supportingUSB 3.1 Gen2. The version of this device tested here is the one with 2 TB of storage. Here are the speeds obtained from a Mac mini M1 via its Thunderbolt 4 socket and from a 2018 Mac mini Intel via its Thunderbolt 3 socket. Remember that the two Thunderbolt 3 and 4 sockets are announced as USB 3.1 Gen2 compatible up to 10 Gbps:

(Speed ​​tests were performed using Blackmagic Disk Speed ​​Test software, available for free on the App Store)

  • Mac mini M1: 722 MB/s write, 692 MB/s read
  • Mac mini Intel: 844 MB/s write, 916 MB/s read

Mac mini M1 records write throughput 15% slower than the Mac mini Intel. In reading, the decline is even more striking: -24%

Samsung X5 External Drive (Thunderbolt)

the Samsung X5 is an external NVME SSD plugging into Thunderbolt and supporting version 3 of this connection. The model tested here is the one with 2 TB of storage, like the T7. Here are the speeds obtained in reading and writing with the measurement software, once again, on Mac mini M1 via its Thunderbolt 4 socket (Thunderbolt 3 backward compatible) and on Mac mini Intel via Thunderbolt 3:

  • Mac mini M1: 2166 MB/s write, 2546 MB/s read
  • Mac mini Intel: 2150 MB/s write, 2314 MB/s read

No big change to note between the two Macs here in writing (difference of 0.74%). In reading, the Mac mini M1 takes the lead (throughput increased by 9%).

Comparative table of Mac mini M1 external SSD speeds

© Workshop 440

Thunderbolt 4 not friends with USB-C

In the end, we realize that the Thunderbolt 4 of the Mac mini M1 has a problem with the USB. It cannot achieve the performance of USB via Thunderbolt 3 on Mac mini Intel. Whereas, as specified above, the two versions of the connectors are announced by Apple as supporting USB 3.1 Gen2 up to 10 Gb/s. In fact, we see it with this test and the data from the previous article obtained on Mac Studio as well, the Thunderbolt 4 does not reach the expected level.

So we’re still thinking, with more and more support, that Thunderbolt 4 on Mac with Apple silicon chip is throttling speeds when used with a USB-C 3.2 Gen2 device.

It is a point to know if you have acquired a machine with M1, M1 Max, M1 Pro or even M1 Ultra chip, or if you plan to do so. For external storage, and if speeds are important to you and your work, it is better to favor a Thunderbolt device rather than USB-C. It would also appear that using a Thunderbolt 3 dock (with USB-C 3.1 Gen2 plugs) plugged into the Mac would result in better performance for an external USB device than if the device was attached directly to the computer via Thunderbolt 4. …

A big thank you once again to the music school of theWorkshop 440 for sharing their measurements.

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