Migration Assistant in macOS has matured over many years from being a fragile tool that often failed to move your identity — your apps, files, preferences, and other data — from one Mac to another. It is now quite reliable and I have used it several times over the years without fail.
But one pain point relates to how quickly files are transferred. Ideally, you want to connect two Macs together with a Thunderbolt 3 or 4 cable. A USB-C plug doesn’t guarantee it’s Thunderbolt – some USB 3.1 and 3.2 cables have USB-C plugs, but when connected between two Thunderbolt 3 ports on Macs, they only transfer 480 Mbps (USB 2.0 speeds) instead of a maximum of 40 Gbps. You can check the cable to make sure that the lightning bolt icon appears on both ends. If not, it can be difficult to verify that you have the correct cable without much detail. Thunderbolt 4/USB4 cables are universal and do not need to be a special type. (This column can help you tell just USB cables and Thunderbolt cables apart.)
What if you’re sure, you plug the cable into both Macs, start transferring Migration Assistant, and the speed is terrible? You can see which method is in use on the Transferring your data screen: at the bottom it should say Current Connection and the method: Wi-Fi, Ethernet, or Thunderbolt. (Ethernet comes in second, offering 1 Gbps; Wi-Fi relies on a peer-to-peer method, which is about 200 times slower than Thunderbolt in my tests.)
In some versions of Migration Assistant, you can click Connection details and view the available methods and how they test for performance in Migration Assistant. If Thunderbolt isn’t listed there, it’s just not being used.
Some users have found that the following can help you transfer at Thunderbolt speeds:
- Instead of using Migration Assistant on both Macs, boot into Target Disk Mode on the Mac you’re transferring from. The Mac you migrate to will recognize it as a source and let you select it. This may work around some macOS issues. (This column tells you how to use Target Disk Mode with Intel or Apple Silicon M-series Macs.)
- Make sure Thunderbolt Bridge Mode is enabled and Connected appears with a green dot in > System Preferences/Settings > Network. If it’s active on both Macs and you see “Not Connected,” it’s likely your cable isn’t working or isn’t the right type. If it’s not there, click the plus sign button (Monterey and earlier) or … (Ventura), choose Add serviceand choose Lightning Strike Bridge of the Couple menu. Click To create.
This Mac 911 article is an answer to a question from Macworld reader Isidore.
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