The requirements are moderate: a USB-C cable that supports Thunderbolt 3 or 4 and a network connection. Organizing a second Mac can be challenging – if necessary, invite Mac user friends over for a movie night. Depending on the amount of data, the backup may take a certain amount of time.
Apple Silicon: Recovery Mode
On a Mac with an M or A processor, activate recovery mode – without it, data recovery will not be possible. An internet connection is recommended for this, but you should be able to start data recovery without it:
- Press and hold the power button until the selection screen appears.
- Click “Options”, click “Continue”.
- Log in with administrator account.
The most frequently used options then appear in the middle of the screen, which you initially ignore. Instead, move your mouse to the top of the screen, click “Utilities” and choose “Share Volume…” from the drop-down menu.
The Share Volume command makes the Mac volumes available to other Macs.
Select the volume whose data you want to recover – usually it is “Macintosh HD”. Enter the administrator’s name and password, confirm your entry with the Enter key and then click on “Share volume…”. Now this Mac is ready to serve as a Thunderbolt network volume for another Mac.
Connect via Thunderbolt
Now establish the physical connection between the two Macs. The USB-C cable should support the “Thunderbolt” standard (3, 4 or 5). You can recognize this by the lightning symbol and a number on one of the plugs. It doesn’t necessarily have to be an Apple Thunderbolt Pro; the Thunderbolt connectors from Anker, for example, also do the job (and cost about half as much). After both Macs are connected via cable, open a Finder window (on the problem-free Mac) and click “Network” in the left column. Then select the name of the problematic Mac, and finally the SSD (usually “Macintosh HD”).
Data transfer
The Finder shows that you are logged in as a guest, but unlike a regular network share, you can access all user folders in this mode. Now copy all important data to keep it as a backup copy in case something goes wrong when restoring macOS. Thunderbolt ensures a fast data rate, but the network protocol slows down the transfer of many small files.
On the second Mac, the shared volume appears as a network share.
Repeat with additional volumes
Remember to back up everyone’s Mac users’ data; Also check the Shared folder to see if there are any common files hidden there. If you have set up additional APFS containers on the defective Mac, you must share them one after the other – “Share volume…” only shares one drive at a time. When all the data is transferred, click Disconnect Volume on your Mac in recovery mode, exit the Split Volume utility, and remove the Thunderbolt cable. Now you can reinstall the system – in most cases the data partition remains unchanged. Only in rare exceptional cases do you have to import the data from the backup again; In such a case, the additional work is clearly worthwhile.
Intel Mac: Target mode
If you have a Mac with an Intel processor from which data needs to be saved, it is best to use Target mode. To do this, hold down the T key while restarting. A Thunderbolt cable also creates the physical connection, which is then used to establish a network connection. Target mode already works on very old Macs with a Firewire connection – but here the target Mac appears as an external drive, without having to go through network shares. Howard Oakley discusses the two options DFU mode and external boot drive in an article on data recovery; he sees them as only having limited applications for successful data recovery.