Thunderbolt Bridge speed is slow - help please

[pgseye]

I have an M2 Mac Studio and an M4 MBP, for which I would like to directly connect to transfer large files. I read that a Thunderbolt Bridge was one way to do that. I bought one of these cables directly from Apple as I know from experience that some third-party cables don't work the way they claim:

https://www.apple.com/au/shop/product/HRGZ2ZM/A/caldigit-thunderbolt-4-usb‑c-pro-cable-1m

When I connect the two Macs, I see a 'Self-assigned IP' connection with a yellow dot on both computers. The speed transfer seems to be limited to about 40 Mb/sec. Thunderbolt 4 should provide much faster speeds than that, right? Have I not set the network connection up correctly?

edit - looking under System Information -> Thunderbolt/USB4, I can see each computer connected to the other at their relevant ports with a suggested link speed of 40Gb/s

 

[joevt]

The problem might be the file systems?
Do an iperf test to test just the network speed between the Macs over Thunderbolt?

 

[pgseye]

The problem might be the file systems?
Do an iperf test to test just the network speed between the Macs over Thunderbolt?

Thank you - that is really helpful.

So I installed homebrew and then iperf and I get the following - which suggests the connection is in fact working at close to the link speed.

I am now beginning to think I am doing something sub-optimal in how I attempting to connect the two computers. I don't know much about networking, but I think have set up the connection in both Finder and Forklift using "smb" protocol. I wonder if that is the problem? If that is the problem, what is the best way to connect (and how do I do it)?

 

[pgseye]

I think I have figured this out now. I was connecting to the wrong IP address (facepalm). The connection now seems to work.

 

[joevt]

So I installed homebrew and then iperf and I get the following - which suggests the connection is in fact working at close to the link speed.

Wow, that's more than I expected. This may be a result of USB4 and improved drivers rather than older Thunderbolt 3 stuff.

I think I have figured this out now. I was connecting to the wrong IP address (facepalm). The connection now seems to work.

Can you get a benchmark for disk I/O over the Thunderbolt connection? Maybe AmorphousDiskMark.app?

 

[Fishrrman]

How "large" are the files you usually transfer?
Unless you're doing this constantly, wouldn't a fast USBc flash drive do almost as well?

 

[wills11]

I think I have figured this out now. I was connecting to the wrong IP address (facepalm). The connection now seems to work.

I'm having the exact same issue—thunderbolt speeds on iperf3 but about 40 MB/s file transfers. I believe I am connected to the correct IP address. The weirdest part is sometimes it will suddenly transfer at full speed — but only in one direction. Unplugging the thunderbolt cable and replugging it in reverts to 40 MB/s.

Did yours completely resolve?

 

[donawalt]

@wills11 this may be a help to try - drawing from my experience using migration assistant, I found that connecting a TB4 cable between two silicon Macs often got very slow speeds - like in the 40-90MB/s area. What I found reliably worked - I read this tip - turn OFF wifi, and unplug any ethernet cables. It seems when the Macs connect they will use some way to decide which connection type to use, that's not always the ideal one. Ever since I started doing that, my TB4 connections are always used to close to optimal speed. Might be worth a try to turn off WiFi and unplug Eth cables and try again.

 

[wills11]

@wills11 this may be a help to try - drawing from my experience using migration assistant, I found that connecting a TB4 cable between two silicon Macs often got very slow speeds - like in the 40-90MB/s area. What I found reliably worked - I read this tip - turn OFF wifi, and unplug any ethernet cables. It seems when the Macs connect they will use some way to decide which connection type to use, that's not always the ideal one. Ever since I started doing that, my TB4 connections are always used to close to optimal speed. Might be worth a try to turn off WiFi and unplug Eth cables and try again.

Thanks! I have found this works, too—but unplugging ethernet cables and turning off WiFi on two machines every time I need to transfer a file is not a workable solution for me.

Setting the "Service Order" in the Networking panel of System Settings is meant to allow one to choose which Network Connection gets priority. Is the issue that this isn't working? Is there a way to fix it?

 

[donawalt]

I never round a way - it does seem to ignore the service order. I wonder if you cold experiment with leaving the TB cable in once it works, then turning WiFiback on/plugging in Ethernet. Be sure and send feedback about the bug (the app is on your Mac), maybe they'll fix it as part of this big "bug fix" MacOS 27 release...