Copy a Time Machine backup for ONE computer to a new external drive

Question

The situation: I'm running Ventura (13.1) on an M1 Macbook Air (2020) and I have a 3 TB external HD, format Mac OS Extended (Journaled), that I use as a Time Machine backup volume for 5 different household computers (not using a LAN -- I physically connect the external drive to each computer when I want to run a backup). It has now filled up, and I have purchased a 5 TB external HD. I want to move the TM Backup for one of my 5 computers onto the new hard drive.

There are multiple articles online explaining how to clone an entire TM backup volume from one external drive to another (many of them explicitly contradicting one another). But I have yet to find any instructions on how to clone the backups for just one computer from an external drive that is used for multiple Macs.

Is this even possible? If not, I guess my next-best solution is to do a fresh, from-scratch TM backup of the chosen computer onto the new drive, and then delete the old backup from the old drive. But this raises a related question: is there a way to delete a backup of just one computer from a TM drive containing backups of multiple machines?

Answer 1

These are the basic steps I followed...

1. Use Disk Utility to format the new external HD as "Mac OS Extended (Journaled)".
2. In Finder, select Get Info for the new external HD and make sure "Ignore ownership on this volume" is not active.
3. Stop any ongoing Time Machine backups and disable "Back Up Automatically" in Time Machine Settings.
4. In Finder, drag and drop the Backups.backupdb folder from your old external HD to your new external HD.
5. In Time Machine Settings, click Select Disk... to select the new external HD and re-enable "Back Up Automatically".

These steps are described with more detail and screenshots in the article titled How to Move Time Machine to a New Backup Drive.

Similar to you, I used these steps this week to save my TM backups for 2 household Macs from a failing 2TB external HDD which I copied to a new 4TB external SSD. After I selected the new disk in Time Machine Settings, I was worried that the next backup was going to take forever (like a new backup from scratch). Instead, it was incremental and quick and that gave me the assurance that the old backups were intact. I also checked by browsing my old backups using Time Machine.

Edit: I re-read your question and noticed that you also found this article. As you figured, this will copy all the backups in the Backups.backupdb folder but each computer will have a unique subdirectory which will contain a dated folder for every backup for that computer. If you only want to copy the backups of one computer and discard the rest, then just copy it all and then delete the subdirectories you don't want. There might be a more efficient way where you manually mkdir Backups.backupdb in the new drive and then drag and drop all the files in the Backups.backupdb and then drag and drop only the folder for the one computer.

Another note is that if your computer names are unique like mine, then identifying which backup subdirectory belongs to which Mac is obvious. If your computer names are the same, then Time Machine will likely just append a number and it may be somewhat confusing which is the right subdirectory. Then you'll need to look inside the backup for some file that is unique to the one computer.