MAC MINI M4 EXternal Drives too slow - just 40MB/s

It is best to get USB3 devices which support UASP for the best transfers and being able to run them on the same dock/hub without interference from slower devices. I'm not entirely sure macOS with the M-series Macs will actually take advantage of UASP....I have seen some mixed information (it is hard to confirm), but the better devices typically support UASP.

In order to get the best speeds and throughput please remember that a bottleneck will ALWAYS occur where the slowest component is which can be cables, enclosure or the drive itself. So if speed is important take time to research .

also, as a general rule OWC (macsales.com) provides about the best peripherals available for Macs!

So the drive connected directly to the Mac and are there no other such connected peripherals, right? No unneeded 3rd party anti-virus apps or usually unneeded 3rd party drive apps that might intervene?

Connected to the rear TB port I assume and not the front ports? I have a NVME in a TB enclosure that should support USB speeds but will only show a speed similar to what you see on the front ports but works fine on the rear TB port.

Is this an "off the shelf" drive or a DIY enclosure/NVMe combo?

For the "off the shelf", what is the brand and model?

If it is a DIY, what brand and model is the enclosure and what brand and model is the NVMe blade?

Also, what is the brand/model of the cable you are using, noting that not all USB-C cables are created equal. Notoriously are charging cables which are only required to support USB2 which is almost never stated on the cables or the packaging.

Note, if this is a DIY, note all enclosure/NVMe combinations work well on all computers. Some may work well on a PC and not work on a Mac, some work on a Mac and won't work on a PC, and some combos can just perform poorly on both.

We need exact details about your external drive (make, model, specs) ... and the cable ... and which USB port on the mini you have it plugged into. And do you have any USB 2.0/1.1 devices plugged in ... like a keyboard, mouse, etc and if so which ports?

Further diagnostics ... post a complete screenshot from System Report > Hardware > USB so we can see the details of what your Mac sees on the USB ports.

Note the front USB ports are USB 3.0 (up to 10Gbps); the rear USB ports are USB 4 (up to 40 Gbps, M4 model; up to 120 Gbps M4Pro model). But the speed also depends on the capabilities of the connected device(s) and the cables.

HelberBimbo wrote:

I'm using a "generic case" for NVME, but as I said, it works well on the notebook, which is an Acer Aspire 5

The case is important, as it contains the interface. What make & model is it?

Just because it works on an Acer Aspire 5 doesn't mean it will necessarily work on anything else.