Mike’s theory echo’d mine, that the Macs are negotiating the TB3 connection at Gigabit speeds. Being over 3x faster was still slower than I expected. I started a new transfer and was now transferring at around 100 MB/s. To test this theory, I unshared the old Mac’s disk, unplugged the TB3 cable from both, plugged both into power, reconnected the TB3 cable, and then re-shared the disk. This made me wonder if because my TB3 cable was charging the other Mac if it had prioritized charging and degraded the data transfer speed to USB-2. I’ve noticed that there are a lot of USB cables that offer a high power rate, but a lower (USB-2 ~480 Mbps) data rate (like Apple’s USB-C charge cables). TB3 has a theoretical speed of 40 Gbps (Giga bits per second) or roughly 5,120 MB/s (Mega Bytes per second). I was using a Belkin ThunderBolt 3 (TB3) cable. My second observation was that my transfer speeds were slow. If no Macs are charging, they’ll pick the Mac with the highest charge and it will start charging the other.Īs far as I’m aware, there isn’t a way to disable this. From my observations, if one Mac is charging, it’ll pass some of that charge on to the non-charging Mac. If one or neither of the Macs are charging, and then you plug the two into each other, they will pick one to charge.

My first observation was that two Macs can charge each other. See the SSH section for my rsync over SSH command.rsync over SSH is, as far as I’m aware, the fastest way to transfer data between two Macs.Macs connect using the Thunderbolt Bridge and get a 169.254/16 address.You can easily connect Macs over ThunderBolt (TB) while booted.I made a few observations and, in the end, changes to how I’ll be doing data migrations going forward. I started this migration the same way that I traditionally have, using Share Disk (formerly Target Disk Mode (TDM)) and rsync. When I setup new computers I tend to opt for setting them up new and transferring the data over “manually” i.e. I got a shiny new M1 Max MacBook Pro this week.

Target mode usb c