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I have a 2021 M1 iMac with a Samsung SSD 860 Evo inside an external Ugreen USB-C enclosure. On my older 27" iMac I get 550mbps read/write. With my M1, I'm only getting 350mbps.
Using MacOS 11.5.2 on both Macs.
Why are the ports extremely slow? I tried both the Thunderbolt ports and the USB-C ports with these drives. It didn't make a difference.
There is a well known issue with the USB implementation on the M1 Macs that causes a large performance drop as compared to Intel Macs or non-Apple laptops. My Samsung T7, for example reaches 1000MB/s on my Intel Mac and barely 660MB/s with the M1 Mac.
This issue has been apparent since soon after the first M1 Macs were released, and, sadly, it appears to be something that Apple is either unable or unwilling to fix.
There is a well known issue with the USB implementation on the M1 Macs that causes a large performance drop as compared to Intel Macs or non-Apple laptops. My Samsung T7, for example reaches 1000MB/s on my Intel Mac and barely 660MB/s with the M1 Mac.
This issue has been apparent since soon after the first M1 Macs were released, and, sadly, it appears to be something that Apple is either unable or unwilling to fix.
It may be your cable. Try the 550mbps cable on the 350mbps device. If they're not the same type cable, you may need to buy a more compatible cable.
For my Samsung T7 external SSDs, the only cable that gives near advertised speeds is the one Samsung included.
External Drives extremely slow on M1 Mac
