I looking for advice to connect 2 Macs over ThunderBolt using multichannel SMB. Has anyone had success configuring this configuration and, if so, could you please provide the details of how you did it.
- Pie Lover
Mac mini (2018)
A word of warning about benching network transfers ...
I've been trying to measure transfer rates over a ThunderBolt connection between 2 Macs. I noticed it's relatively easy for the interface to be switched to GigE or Wi-Fi when the disk shares are referenced by their volume name.
One remedy to to simply to set other interfaces to Inactive (on both devices). Another approach is to use Finder>Go>Connect to Server using the IP address of the ThunderBolt link connected to the share. For example:
In either case, you can check the estimated transfer rate in realtime using the Activity Monitor:
- Pie Lover
I’ve been experimenting with different configurations. Below is my best result to date. I found that the ThunderBolt Bridge transfer is faster when reading from the Intel Mac than when writing from the M2 Mac. Overall, I would say that the performance is usable but disappointing given the theoretical ThunderBolt 3/4 speed of 40 Gbps.
Photos Library backup from M2 Mac mini to Intel Mac mini using point-to-point ThunderBolt Bridge
45.16 GB Photos Library -> 44.21 GB Apple Archive – 2:57 (on M2)
SMB transfer of Apple Archive – 2:03 (~ 360 MB/s, ~ 3 Gbps) (copy initiated from Intel)
Apple Archive -> Photos Library – 5:10 (on Intel)
Total transfer time: 10:10, Effective transfer rate: 74 MB/s
Hardware Setup
Mac mini 2023, Chip Apple M2, Memory 16 GB, macOS Sequoia 15.3.1, Source disk: Samsung 2TB T7 SSD connected via 10 Gbps USB 3.1 Gen 2 (via TB4 port on TB4 hub)
Mac mini 2018, 3 GHz 6-Core Intel Core i5, Memory 8 GB, macOS Monterey 12.7.4, Target disk: Samsung 500 GB SSD connected via 10 Gbps USB 3.1 Gen 2 (via TB3 port)
ThunderBolt Bridge, M2: TB4 port, Intel: TB3 port, ~3 foot TB4 cable, optimized SMB settings (but not multichannel)
Your 74MB/s "effective transfer rate" isn't the network transfer rate. It appears to include creating an archive file & importing into Photos. Further, the transfer appears to have involved USB drives on each end, so the overall transfer speed would be limited by the speed of USB 3.1 Gen 2 (10Gbps). You also had a TB hub in the mix. All of which impose time & speed constraints on the transfer. Plus it was a Photos Library, which is known for having slow transfers.
What was your reason for creating an Archive file?
If I read your note correctly, the transfer between your Macs was 360 MB/s, about 3 Gbps. Given that the source & target drives were both USB 3.1 Gen 2 and knowing it was a Photos Library, I'd say you did pretty good. But under no circumstances were you ever going to get 40 Gbps end-to-end out of this.
You might want to measure a Thunderbolt 3/4 file transfer using a file on the internal SSD of your source Mac to the internal SSD of your target Mac for a better understanding of the actual TB transfer rate between the two Macs.
Keep in mind that all these transfer rates (10Gbps, 40 Gbps) are maximums in the specs, they are not guarantees of those rates in real life.
The Samsung T7 has up to 1050 MB/s sequential reads and up to 1000 MB/s sequential writes. That is potentially up to 8.4 Gbps (involving sequential access) from the USB-C 3.1 Gen 2 10 Gbps rated storage minus any non-sequential activity and associated overhead that you mentioned.
Thanks for taking the time to reply. While your points are well-taken, I still think that even 360 MB/s is not very close to the typical transfer rates for such drives without intervening network (but of course still connected using USB 3.1 Gen 2). My expectation was to see rates above 500MB/s and, hopefully, approaching 1 GB/s. The internal SSDs are indeed significantly faster than external SSDs (my Photos Library resides on an external (T7) SSD).
The Archive Utility actually accelerates the overall transfer as it converts the Photos Library package format into a single file. For example, my 45 GB Photos Library includes over 17,000 images but contains some 82,000 items. The Archive Utility is multi-threaded and is designed to run efficiently on multiple cores. Using Archive on the M2 is quite fast but less so on the Intel Mac mini (despite its 6 cores).
I've been told that SMB is not designed specifically for speed. macOS (since Big Sur) supports multichannel SMB but I'm not certain if multichannel can be used for Mac-to-Mac transfers. Apple support was not helpful in clarifying the matter.
BTW, the ThunderBolt 4 hub supports 3 TB4 ports (in addition to the host TB4 port) so each port has lots of headroom when connected to a USB 3.1 Gen 2 device. Granted that there will be some additional latency compared to having no hub.
- Pie Lover
Thanks for pointing out these factors. I realize that the SSD transfer rate will limit the overall transfer speed but I didn't expect the ThunderBolt Bridge to be so much of a limitation. BTW, I suspect that the reads and writes to the source and destination SSDs (especially on different machines) may be overlapped.
- Pie Lover
Thanks for the link.
You're welcome. I hope it works out for you.
How can I configure multichannel SMB between 2 Macs
