Transfer Time Machine backup to a new external drive

Time Machine Backup Transfer — macOS 12.7.6

1 - For a Mac mini running macOS 12.7.6 (Monterey), Apple does not provide a documented or supported procedure for transferring an existing Time Machine backup history from one external drive to another external drive.

This distinction is important. 

2 - It is possible to encounter instructions on the internet describing methods involving disk cloning, rsync, asr, tmutil, Disk Utility, or other third-party utilities. 

3  - However, those should not be confused with an Apple-supported Time Machine migration procedure. Unless a method can be demonstrated to preserve the complete Time Machine history and remain fully recognized and usable by Time Machine, it should be regarded as an unsupported technique, not as an official solution.

4 - Apple's documented approach when moving to another Time Machine disk is to connect the new disk and designate it as a Time Machine backup destination. Apple also supports using multiple backup disks.

5 - Consequently, the safest Apple-supported arrangement is:

Old external drive: Leave it intact and retain its existing Time Machine history.

New external drive: Configure it as a Time Machine backup disk.

Future backups: Allow Time Machine to create backups on the new disk.

Old history: Continue to access the old disk when you need to retrieve an older backup.

6 - This approach does not transfer the old Time Machine history to the new disk. Instead, it preserves the old history on the original disk while establishing a new backup history on the new disk.

7 - Do not erase the old Time Machine disk merely because the new disk has been connected and configured.

A - ➡️ If preserving the existing backup history is important, the old disk should remain untouched until you are completely satisfied that you no longer need it. ⬅️

B - Likewise, simply seeing a Backups.backupdb folder or other Time Machine-related files on a newly copied disk should not by itself be considered proof that the new disk is a valid replacement Time Machine backup.

8 - For macOS 12.7.6, the answer to:

"Can I move my existing Time Machine backup history from External Drive A to External Drive B using an Apple-supported procedure?" is no. Apple does not document such a migration procedure.

9 - The Apple supported solution is to keep the existing Time Machine disk intact and configure the new disk as a Time Machine destination.

10 - If the objective is specifically to retire the old disk while preserving its entire historical Time Machine backup set on the new disk, that becomes a separate technical question involving methods that are not documented by Apple and should therefore be treated as unsupported.

Apple references:

Apple — Use Time Machine to back up your Mac

Apple — Use Time Machine to back up to multiple disks

Apple — If the Time Machine backup disk is full

Apple — Time Machine troubleshooting

Transfer your Time Machine backup to a new drive safely by using macOS Finder to copy the backup folder, ensuring you preserve file permissions and do not disrupt backup history. Connect both drives, format the new drive as Mac OS Extended (Journaled) or APFS using Disk Utility, and copy the root folder named after your Mac. 

Steps to Transfer the Backup

• Connect both the old and new external hard drives to your Mac Mini.
• Open the old external hard drive in Finder.
• Find the folder named with your Mac's name (containing the Backups.backupdb directory).
• Drag and drop that main backup folder from the old drive to the new drive.
• Wait for the copy process to finish completely. Large transfers can take many hours.