Open Radar

 
Migration Assistant can hang interminably when a Thunderbolt cable is plugged in mid-way.
FB9864975 — macOS

Basic Information

Please provide a descriptive title for your feedback:
Migration Assistant can hang interminably when a Thunderbolt cable is plugged in mid-way.

Which area are you seeing an issue with?
Installation/Setup/Migration/Recovery

What type of issue are you reporting?
Application Slow/Unresponsive

Details

What does the installation/setup/migration/recovery issue you are seeing involve?
Migration during installation

What build of macOS were you upgrading from?
macOS 12.1

What were you migrating from?
Another macOS installation

What time was it when this last occurred? (Example: 12:00 pm EST 02/14/2018)
3:00pm EST 01/26/2022

Description

Please describe the issue and what steps we can take to reproduce it:
Migration Assistant can hang interminably when a Thunderbolt cable is plugged in mid-way.

I attempted to migrate data between two A2442 MacBookPro18,4 (14” MacBook Pro 2021) machines. The source machine was running 12.1 and the destination machine was running 12.2.

1. Connect the two machines via Ethernet.
On the source machine, I had an Apple Thunderbolt2 Gigabit Ethernet adapter plugged in to a TB2/TB3 bridge.
On the destination machine, I had a Anker A8313 USB-C Gigabit Ethernet adapter
Between them was a 4’ ethernet cable.
2. Start Migration Assistant on the source machine.
3. Start Migration Assistant on the destination machine.
4. After a few hours of data transfer, Migration Assistant’s estimate says many hours are left.
5. Migration Assistant regularly displays, “Connecting a Thunderbolt cable may transfer data faster.”
6. I went to the Apple Store and purchased a brand new 0.8m Apple Thunderbolt3 cable.
7. I plugged in the Thunderbolt3 cable.

Migration Assistant hung. The number of files stopped increasing and the time estimate did not update.
It appears the transfer has hung.

CONCLUSION: Plugging in a Thunderbolt cable in the middle of a migration is not reliable.
Unfortunately, Apple’s text appears to recommend this (“Connecting a Thunderbolt cable may transfer data faster.”).

THEREFORE EITHER:
(a) Migration Assistant should be robust to changes in Thunderbolt connectivity in the middle of a transfer. This is the preferred option.
(b) Migration Assistant should change the wording of the recommendation to not suggest connecting a Thunderbolt cable during the transfer is OK. For example, “Thunderbolt may transfer data faster. Consider terminating the transfer, plugging in a thunderbolt cable, and restarting it.” This is not the preferred option.

I recognize this is difficult to test and there is not a clear reproduction case. It all felt very janky and unreliable.