Most M1 Mac Thunderbolt 4 ports don't support USB 3.1 Gen 2's 10Gb/s transfers, tests reveal

Pro users of the M1 Mac are reporting disappointing transfer speeds from external SSDs, and testing seems to indicate that most M1 Mac Thunderbolt ports don't support USB 3.1 Gen 2, meaning they can't offer transfers up to 10Gb/s Speeds are as expected from Thunderbolt 4.

Testing was conducted on a 2021 16-inch MacBook Pro M1 Max and a 2022 Mac Studio M1 Max

We have discussed many times the different USB-C standards, devices and the mess and confusion caused by cables.

There is also a significant difference between theoretical maximum speed and actual maximum speed.

But testing shows that most M1 Macs don’t support the USB 3.1 Gen 2 standard, making Thunderbolt transfer speeds slower than both theoretically and practically.

Eclectic Light summarizes the bottom line of current speeds provided by different standards.

• USB 3.0 and higher supports SuperSpeed ​​USB at 5 Gb/s.
• USB 3.1 Gen 2 adds 10 Gb/s SuperSpeed.
• USB 3.2 adds dual-channel SuperSpeed ​​at 10 and 20 Gb/s.

M1 Mac Thunderbolt 4 Ports Tested

Eclectic Light's Howard Oakley ran a series of tests with two M1 Macs:

• Apple Mac Studio Comes with M1 Max, 32 GB RAM, 2 TB internal SSD, connects to Apple Studio display;
• Apple MacBook Pro 16-inch, 2021 comes with M1 Pro, 32 GB RAM, 2 TB internal SSD, uses its internal display .

There are two ways to establish the speed capabilities of a data connection. The first is to look at the theoretical speed reported by the machine. Oakley first tested using an Intel Mac to verify that his test SSD and cable were absolutely compatible.

Each is connected to an Intel Mac (including iMac Pro) and has been verified to have a SuperSpeed ​​10 Gb/s connection to those Macs.

Cables used include certified Thunderbolt 4 models, as well as the USB-C (data) cable provided with the box. Again, each is verified by establishing a SuperSpeed ​​10 Gb/s connection to an Intel Mac.

The connection speed is read from the SSD entry in the USB data given in System Information.

Second, measure the speed in real life.

Transfer rates were measured using my free application Stibium 1.0 (55) which wrote a total of 160 files ranging in size from 2 MB to 2 GB to files on the SSD being tested folder and then read those same files back (series write and series read tests, see Stibium's help reference for details). Follow a procedure detailed as the "gold standard" test.

Oakley compared Intel and M1 Macs again and found that the new machines were actually slower.

The key here is that the fastest storage devices run about half the expected speed; this limitation seems to exist in all M1 Macs; using Thunderbolt 4 Cable connecting USB-C devices to the front USB-C port on Mac Studio Max results in speeds that are 10% lower than expected; even the latest Mac Studio models don't support USB 3.1 Gen 2. Currently, to my knowledge, it appears that the Thunderbolt ports in any M1 model since its release in November 2020 do not fully support 10 Gb/s SuperSpeed ​​in USB 3.1 Gen 2, at least for For SSD.

M1 The only port in the Mac that currently appears to fully support USB 3.1 Gen 2 is the one on the front of the Mac Studio Max.
• The M1 Mac's Thunderbolt port does appear to support 10 Gb/s SuperSpeed ​​in USB 3.2 devices.
• For SATA/USB-C storage, the impact on performance is limited, reducing transfer speeds from the expected 500 MB/s to 400 MB/s. For external storage used to store Time Machine backups, this probably won't have any significant impact, as backup I/O will be limited anyway.
• The biggest impact is likely to be on external storage with transfer speeds approaching 10 Gb/s, such as RAID arrays and NVMe SSDs with USB 3.1 Gen 2 instead of Thunderbolt 3. In these cases, the expected transfer rate of 900 MB/s may be reduced to less than 500 MB/s, doubling the time required to read or write the file.
• Users of USB 3.1 Gen 2 devices should connect them to a USB port on a Thunderbolt 3 Dock or Studio Display where they should perform better.
• This flaw appears to be present in all M1 Macs for nearly 18 months. If it was a bug in the firmware of Fabric Core responsible, it should have been fixed a year ago. If the fault was with the M1 series chips, Apple should have notified users and confirmed the compatibility of these ports.
• Apple needs to investigate why using a Thunderbolt 4 cable to connect a USB-C device to the front USB-C port on the Mac Studio Max results in very poor performance, less than 10% of the expected transfer rate.
• The lack of support for 10 Gb/s SuperSpeed ​​in USB 3.1 Gen 2 is arguably the most egregious failure in a very successful transition.

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