What is the Real-world Data Transfer Rate of a Thunderbolt 4 port connected to PCIe NVMe 4.0 SSD?

Question

Level 1

4 points

What is the Real-world Data Transfer Rate of a Thunderbolt 4 port connected to PCIe NVMe 4.0 SSD?

What is the Real-world Data Transfer Rate of a Thunderbolt 4 port connected to an external PCIe NVMe 4.0 SSD?

Is there any real-world benefit of using a Thunderbolt 4 port, on a Mac mini M2 Pro, to connect to a Thunderbolt 4 port, on a OWC miniStack STX?

The OWC miniStack STX would contain:

One (1) 6.0TB Seagate Exos 7E8 HDD and either

One (1) 2.0TB Aura Ultra IV PCIe 4.0 NVMe M.2 2280 SSD

with unknown Read / Write specs

-or-

One (1) Crucial T500 2TB PCIe Gen4 NVMe M.2 2280 SSD

with Read speeds up to 7,400MB/s  & Write speeds up to 7,000MB/s

I have read that a Thunderbolt 4 port is spec'd at up to 40 Gb/s (or 5000 MB/s)?

But isn't a PCIe 4.0 (x4) port/connection only running at approximately 8 MB/s?

If so, is the transfer rate limited to speed of the PCIe port/connection?

If the transfer rate is going to be so limited would it be more sensible to use a less expensive enclosure for the SSD and HDD, one which uses a USB 3.1 Gen 1 or Gen 2 connection to the Mac mini M2 Pro?

Background notes:

I have read conflicting descriptions for the Date Transfer Rate of PCIe NVMe 4.0 SSDs.

I have read that current SSDs use 4x Lanes for approximately 8 GB/s Transfer Rates.

But I have also read that the OWC miniStack STX's M.2 bay connection only supports One (1) Lane, with only 770 MB/s real-world use.

Also, I have read that "to take advantage of PCIe Gen 4, your CPU, motherboard, and PCIe devices must all support PCIe Gen 4".

Yet I haven't found any specs that state that Apple Mac(s) supports PCIe 4.0.

Does this CPU, etc support requirement even matter, when the PCIe 4.0 device is an external device connecting by way of a Thunderbolt 4 port and not plugged into the motherboard?

Mac mini, macOS 13.5

Posted on Nov 4, 2023 8:46 PM

Reply

Answer 1

Best reply

woodmeister50

Level 6

19,753 points

Nov 5, 2023 5:07 AM in response to FrankPerry

Real world results on transfer speeds depends on a lot of factors: the actual NVME drive, how the drive works with the enclosure, and how well the combo works with a particular OS and computer.

Generally speaking, the max transfer data transfer speeds I have seen on the internet via Thunderbolt3/4 or USB4 with an NVME mated with the right enclosure is around 2800 MB/s read/write with just the right combination of everything. Generally, one can expect reads in the 2300-2600 MB/s and writes in the range of 1500-2300 MB/s, all of which is highly dependent on the above combinations expected. Also, I believe that the Thunderbolt spec dedicates a certain minimum BW for video so the remaining BW is for the rest of the devices.

On Macs, the USB 3.2/3.1 speeds max out at about half that.

The "combo" issue is not just Mac related either. You can have a combo that screams on a Mac but is a slug on a PC and visa versa.

So, some points:

-it doesn't pay to get some of the super speed SSDs since the they only get close to those speeds when directly connected to an internal PCI bus of a computer. The controllers for translating to and from Thunderbolt take a toll.

-For sustained speed transfers, to simplify things, these SSDs have a buffer between the controller and the actual NAND storage cells. So, depending on the size of that buffer, the advertised speed may only work for a short time and when the buffer fills can drop drastically. Some can drop even below USB2 speeds.

-Some drive enclosure controllers don't always play well with the NVME depending on the controller on it.

-Also, some combinations may work great on some Mac models and some may be meh on other Mac models. It seems the Pro and Max versions of the M1/2/3 get better performance than the base M1/2/3 models, particularly on write performance.

So, do some research on the devices you are trying to mix together to determine the best combination for your particular setup.

Reply