Mac Mini M4 Pro Thunderbolt 5 speed issues.

I have the same issue - thunderbolt 3/4 external SSD drives much slower on the M4 Pro mini, compared with both my m3 MacBook and old intel retina iMac

I don't think the "its all on one shared bus" theory is correct through. Under system information, I can see

• Thunderbolt/USB4 Bus 0
  • Sabrent Enclosure
• Thunderbolt/USB4 Bus 1
  • Apple Studio Display
• Thunderbolt/USB4 Bus 2
  • Portable SSD X5

Both SSDs used to do around 2500. Now they are <1000 on Blackmagic speediest the first pass, then around 500Mb/sec on subsequent passes. Apple Studio Display is the only other new addition. Very concerning, given the reliance on Thunderbolt 5 ports to get around the outrageous upgrade pricing for internal SSD space.

Note that with the plain M1 chip, while it supports USB4 is only Thunderbolt3.

With that said, you could very well have an issue with the controller in the Sandisk drive not playing well with Thunderbolt 5 protocols and may possibly need a firmware update. It could also be using an older generation Thunderbolt controller that simply does not recognize the Thunderbolt 5 as a Thunderbolt connection and therefore reverts to the slower USB spec.

You may want to reach out to Sandisk or WD (which ever the two are calling themselves after the merger) with the issue.

fangjnr wrote:

I am also getting really slow speeds from any drive connected to my Mac Mini M4 Pro. A Thunderbolt 4 enclosure capable of 40gps with an NVME m2 drive that should be able to do 7200 mbps is only getting speeds about 1/4 of that. It's just crawling about 1000 mbps on a fresh new drive with all new cables and enclosure.

It may or may not be the issue but what enclosure is being used and what brand/version of NVMe is being used?

It should be noted that not all enclosure/SSD combinations work well with all computers. This is true not just for Macs but also PCs. Even from Mac to Mac, some combos work well on some Macs but not on others.

As an aside, the best speeds to be expected from any Thunderbolt4 enclosure under the most ideal situations will be around 3200 MB/s and generally end up in the 2200-2700 range. Using a 7200 MB/s NVMe will not change his fact. Just added this as an explanation of what you could expect to see.

IMO, there are two buses, 1 for the two front USB 3 ports and 1 for the three TB5 ports in the rear. I’m also guessing monitors connected to any of these ports have higher bandwidths pre-assigned. Which explains support for multiple monitors - they’re guaranteed bus bandwidth by design unlike external disks who’ll get whatever’s left.

SanDisk – SanDisk Professional PRO-G40 SSD (exFAT) - 1TB

SanDisk claims that this is a dual-mode device, which can connect via Thunderbolt 3 or USB 3.2 Gen 2.

"Our most productive drive yet delivers turbocharged speeds up to 3000MB/s read and 2500MB/s write via Thunderbolt™ 3 and up to 1050MB/s read & 1000MB/swrite via USB-C™."

I believe that USB 3.2 Gen 2 – without the "x2" – is another name for USB 3.1 Gen 2.

The Thunderbolt 5 ports on the M4 Pro Mac mini presumably should be backwards compatible with Thunderbolt 3 and 4. So I would expect this drive to

• Connect using Thunderbolt 3 to any of the three USB-C ports on the back of the M4 Pro Mac mini
• Connect using USB 3.1 Gen 2 to either of the two USB-C ports on the front of the M4 Pro Mac mini

Do you expect Thunderbolt 5 speeds from a Thunderbolt 3 device? Also, remember the speeds advertised are always PEAK speeds and often are not consistent speeds. You can test with TB5 cables however the bottleneck is always going to be the weakest link in the chain, in your case that could be Thunderbolt 3 AND cables however, my hunch is the Thunderbolt 3 device you are using.

I have several WD NVME drives in TB enclosures. I see the same speed on my Mini M4 pro using a TB3-TB5 cable so not sure why you would have any issues unless there is something with the Sandisk drive itself. I have one of my TB4 enclosures that reads fine on my M4 but slow on my Intel 27" iMac (has TB3 ports) so I assume there is some chip difference in the TB4 enclosure that does not play well with the TB3 protocol.

Understood however that expectation may be unrealistic. As I mentioned earlier "Also, remember the speeds advertised are always PEAK speeds and often are not consistent speeds." I suspect the problem may be on the Sandisk side.

I am also getting really slow speeds from any drive connected to my Mac Mini M4 Pro. A Thunderbolt 4 enclosure capable of 40gps with an NVME m2 drive that should be able to do 7200 mbps is only getting speeds about 1/4 of that. It's just crawling about 1000 mbps on a fresh new drive with all new cables and enclosure.

Something feels really off

One question might be whether all of the Thunderbolt ports are on one bus, or whether there are two or three Thunderbolt buses. Running System Information might help here. If there are two or three buses, one might try placing the high-speed SSD on a port associated with a different bus than the USB-C port used to connect the display.

I stand corrected on the number of buses (thanks).

However, my point was that Apple isn’t selling bandwidth wholesale but ports and interfaces mainly to connect suitable displays and boring plain-vanilla USB peripherals.

How the Mac allocates bandwidth isn’t up to users - it’s design internal and probably device discriminatory. It’s the same concept Macs use to allocate power - users don’t have a right to what the USB spec says, it depends on the device being connected to.

In particular, external SSDs which don’t get any mention in the spec or elsewhere - how bandwidth gets allocated to these devices isn’t something in your control, it’s up to the vendor to resolve. They need to test and certify performance with Macs and publish that in their spec including supporting it fully i.e. take ownership.

Good luck!