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What type of cable would I need for USB-C to USB-C 40gbps tranfers

wiffle

wiffle

macrumors regular
Original poster
Apr 5, 2017
167
78
i.e. copying complete hard disks from 2016+ versions of MBPs?

I reckon the included USB-C charging cable that can connect two MBPs is only capable of USB2 speeds which is significantly slower than USB3. Does Apple even have any of these cables (TB3 to TB3 capable of 40gbps?)

Links to ones that could support TB3 / USB3 speeds would be great. Thanks!
 
You are correct the supplied cable is only a power cable and USB2 and does not support target disk mode

I think the Apple store Belkin cable is a TB3 cable but only up to 60w so it will not charge your 15" MBP the same as the supplied power cable
 
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poematik13 said:
You need a TB3 cable to get the full 40gb/s speed.

https://www.apple.com/shop/product/HKK12ZM/A/belkin-thunderbolt-3-cable-05-m

Apple doesn't sell one (?) so you have to go 3rd party (Belkin). They also don't sell a 1st party USB C 3.1 gen 2 (10GB/s) cable which is weird. Apple only makes a USB C to USB C charge cable which as you've noticed is limited to power + USB 2.0 speed.
Click to expand...

Yeah those cables are short. The one I linked is a little longer but yeah the tech now prevents a longer tb3 cable.
 
Thanks all. So this is a bit strange: I picked up a Belkin TB3 cable to do a 2016 MBP to another 2016 MBP migration. Both 15" so I'm sure they're TB3 ports. The max speed I got during the transfer was about 200MB/s, which is basically like USB2 speeds... At the claimed 40Gbps, I should be almost transferring at 5000MB/s at its peak but I'm nowhere near that.

Any thoughts as to why this is the case? For what it's worth, I set up the original as a target disk and used migration assistant on the new.

Edit: if I weren't connected to a discrete power source during the transfer, would that have affected the speeds?
 
wiffle said:
Thanks all. So this is a bit strange: I picked up a Belkin TB3 cable to do a 2016 MBP to another 2016 MBP migration. Both 15" so I'm sure they're TB3 ports. The max speed I got during the transfer was about 200MB/s, which is basically like USB2 speeds... At the claimed 40Gbps, I should be almost transferring at 5000MB/s at its peak but I'm nowhere near that.

Any thoughts as to why this is the case? For what it's worth, I set up the original as a target disk and used migration assistant on the new.

Edit: if I weren't connected to a discrete power source during the transfer, would that have affected the speeds?
Click to expand...

Hmm. Maybe the migration assistant doesn't utilize the faster bandwidth. Although it should/could be faster. 200 mb seems slow.
 
200MB/s as displayed by the migration assistant is 200 Mega Byte / second, so closer to 2GBit/Sec. I get a peak of 90 MB/sec with USB 3 (but overall quite a bit less). Also, the transfer is not "cable limited" for small files. You will notice faster transfers for larger files (e.g. in "Applications") .
 
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underattack said:
200MB/s as displayed by the migration assistant is 200 Mega Byte / second, so closer to 2GBit/Sec. I get a peak of 90 MB/sec with USB 3 (but overall quite a bit less). Also, the transfer is not "cable limited" for small files. You will notice faster transfers for larger files (e.g. in "Applications") .
Click to expand...

Sorry I don't understand what your trying to say. How is 200 Mbps equal to 2 Gbps?
 
Truefan31 said:
Sorry I don't understand what your trying to say. How is 200 Mbps equal to 2 Gbps?
Click to expand...

Apple's migration assistant displays the speed in "MB" (mega byte), not "MBit" (mega Bits). 1 Byte = 8 Bit, and there are likely so,e parity bits and other overhead so that is why I multiplied the speed by 10
 
underattack said:
200MB/s as displayed by the migration assistant is 200 Mega Byte / second, so closer to 2GBit/Sec. I get a peak of 90 MB/sec with USB 3 (but overall quite a bit less). Also, the transfer is not "cable limited" for small files. You will notice faster transfers for larger files (e.g. in "Applications") .
Click to expand...

Yep - you have your calculations correct.. but the 2 Gbps is still quite a bit off from the 40 Gbps advertised.. perhaps others who mentioned that Migration Assistant might not be able to utilize all the bandwidth correct.
 
As mentioned earlier, dividing by ten gets you a more realistic megabytes/second from megabits/second.

You're never going to get 4GB/sec if your transferring data from files because the SSD in the recent MBP's are more like 2GB/sec. - fast, but not as fast as Thunderbolt 3.

If you're using Migration Assistant, take a look at System Preferences, under Networking and see if the Thunderbolt Bridge is active. This will need to be done while both computers are connected. If so, then my guess is that the limitations in speed is due to both computers acting like they're connected via an Ethernet cable.

If you connect two computers on a regular basis and want more speed, you might want to try target disk mode and see if it's faster.
 
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treekram said:
If you're using Migration Assistant, take a look at System Preferences, under Networking and see if the Thunderbolt Bridge is active. This will need to be done while both computers are connected. If so, then my guess is that the limitations in speed is due to both computers acting like they're connected via an Ethernet cable.

If you connect two computers on a regular basis and want more speed, you might want to try target disk mode and see if it's faster.
Click to expand...

Yep, all true. TB3 Networking runs at 10 Gbps.
[doublepost=1497761536][/doublepost]
Truefan31 said:
http://www.j5create.com/our-products/usb-type-c-cables/jucx01.html
Click to expand...

Love their cables but what a weird company name.
 
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treekram said:
As mentioned earlier, dividing by ten gets you a more realistic megabytes/second from megabits/second.

You're never going to get 4GB/sec if your transferring data from files because the SSD in the recent MBP's are more like 2GB/sec. - fast, but not as fast as Thunderbolt 3.

If you're using Migration Assistant, take a look at System Preferences, under Networking and see if the Thunderbolt Bridge is active. This will need to be done while both computers are connected. If so, then my guess is that the limitations in speed is due to both computers acting like they're connected via an Ethernet cable.

If you connect two computers on a regular basis and want more speed, you might want to try target disk mode and see if it's faster.
Click to expand...

So when I did the transfer, I had my old Mac set on Target Disk mode and yielded the speeds that I noted in the OP. Is this what you're referring to?
 
Truefan31 said:
Certified and tested usb 3.1 gen 2 to support 100w power and 10gb data speeds.
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Can you provide a citation? No offense, regardless of what they write, The Wirecutter is IMO a bunch of paid shills. For the cable you quoted, I checked the product portal, and it's not "certified", rather, it's not in their database. I also checked for j5create in the certified company list, and the portal returned "No records matched your search." - ixnay on the j5say. Reads like junk to me - I've provided two links backing up my check. Show me otherwise…

All Results for: JUCX01
 
wiffle said:
So when I did the transfer, I had my old Mac set on Target Disk mode and yielded the speeds that I noted in the OP. Is this what you're referring to?
Click to expand...

If you used the instructions in the following link you used target disk mode.
https://support.apple.com/en-us/HT201462

If you used Migration Assistant, from what I'm seeing in the Apple documentation, you use target disk mode when using Firewire or using Mountain Lion or earlier, which wouldn't be possible with the 2016/2017 MBP's. In either case, if you want to find out, do what you did earlier and check the System Preferences -> Networking.
 
campyguy said:
Can you provide a citation? No offense, regardless of what they write, The Wirecutter is IMO a bunch of paid shills. For the cable you quoted, I checked the product portal, and it's not "certified", rather, it's not in their database. I also checked for j5create in the certified company list, and the portal returned "No records matched your search." - ixnay on the j5say. Reads like junk to me - I've provided two links backing up my check. Show me otherwise…

All Results for: JUCX01
Click to expand...

https://docs.google.com/spreadsheets/d/1vnpEXfo2HCGADdd9G2x9dMDWqENiY2kgBJUu29f_TX8/pubhtml#

Certified and recommended by Nathan K and benson Leung. Model JUCX01. USB 3.1 gen 2. 10 gb/100w/5amp capable.

Wonder if it'll work with dash charging for a one plus 3t.
 
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treekram said:
If you used the instructions in the following link you used target disk mode.
https://support.apple.com/en-us/HT201462

If you used Migration Assistant, from what I'm seeing in the Apple documentation, you use target disk mode when using Firewire or using Mountain Lion or earlier, which wouldn't be possible with the 2016/2017 MBP's. In either case, if you want to find out, do what you did earlier and check the System Preferences -> Networking.
Click to expand...

Yes - those are the exact steps I used to transfer the files between old 2016 and new 2016. I would not have been able to load up System Preferences --> Networking on the new 2016 as it was a brand new unit which used Migration Assistant right out of the box.

Target Disk mode is available on the 2016/17 MBPs: "
Target disk mode on MacBook Pro with Thunderbolt 3 (USB-C) ports
You can use target disk mode to transfer data between MacBook Pro models with Thunderbolt 3 and other Mac computers.

To use target disk mode between a MacBook Pro with Thunderbolt 3 and another Mac notebook's USB-C port, connect the two computers with a USB-C cable such as the Belkin 3.1 USB-C to USB-C Cable."
 
wiffle said:
Yes - those are the exact steps I used to transfer the files between old 2016 and new 2016. I would not have been able to load up System Preferences --> Networking on the new 2016 as it was a brand new unit which used Migration Assistant right out of the box.

Target Disk mode is available on the 2016/17 MBPs: "
Target disk mode on MacBook Pro with Thunderbolt 3 (USB-C) ports
You can use target disk mode to transfer data between MacBook Pro models with Thunderbolt 3 and other Mac computers.

To use target disk mode between a MacBook Pro with Thunderbolt 3 and another Mac notebook's USB-C port, connect the two computers with a USB-C cable such as the Belkin 3.1 USB-C to USB-C Cable."
Click to expand...

According to what I see in the Apple documentation, you didn't have to start the old Mac in target disk mode for Migration Assistant to work. However, it doesn't say that Migration Assistant won't work that way. If the way that you used Migration Assistant used the Thunderbolt Ethernet bridge, then that would account for less much slower than 40Gb/sec. speeds (although 200MB/sec. is more than I would expect, but that's another issue to ponder). (By the way, USB2 is more like 40MB/sec.) The way to know for sure is for you to replicate what you did and see if the Thunderbolt Ethernet bridge is active (this would be done on the computer which is running Migration Assistant). Migration Assistant can be run as a stand-alone app outside of the initial setup and going through the steps and stopping just before one initiates the actual transfer - that's when to check for the Thunderbolt Ethernet bridge. If this isn't possible, then somebody else would have to try that (having one 2016/2017 MBP in target disk mode, running Migration Assistant on another 2016/2017 MBP). It looks like kilawat tried this but I don't know if one of the computers was in target disk mode.
 
wiffle said:
but the 2 Gbps is still quite a bit off from the 40 Gbps advertised..
Click to expand...
They don't advertise 40Gbps for network file transfers. 40gbps is the peak (theoretical) transfer speed across the TB port itself. Real-world usage scenarios mean speed is going to be less, and maybe much less depending on what you're doing. Reading files off the disk and shoving them across the TB port means involving a lot more parameters than just the thunderbolt interface itself. Disk subsystem, I/O caching and file system efficiency, and so on. As another poster mentioned, reading/writing smaller files off a drive is less efficient than large files, so your transfer speed would go down in that case. OS partitions tend to be rather packed with smaller files, btw. :)

Also, the thunderbolt interface probably doesn't have much of, or even any hardware acceleration for ethernet networking, as that is not its primary function. That means the CPU would be responsible for packetizing the data, generating headers, calculating CRCs and so on - very intensive stuff at the data rates involved.

Check the CPU activity monitor if one or more CPU cores are maxed out during transfer. If you have maxed CPU cores, then this is likely your bottleneck. If you regularly plan on transferring a lot of data between your computers, maybe you would have better luck with a dedicated thunderbolt 3 10G ethernet adaptor, if any such are available. Such an adaptor would most likely have full CPU offload capability; you'd have to check manufacturer's claims and specs to make sure. :)
 
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