Repair Time Machine after Computer Upgrade or Logic Board Fix

Some weeks ago, I got a new MacBookPro and installed the new system using my Time Machine backup disk - great feature! After installation, it was the very same system, I was working at before - except for some minor changes (like the MAC address, etc). Anyhow, Time Machine did not want to re-use the old Time Machine backups on my new laptop and hence started a new directory. I left the old directory on my disk, even without being usable at all and today, I found a page, which is coping with a very similar problem and adapted it to my situation.

The basic steps are summarized in the following. The Time Machine backup disk is assumed to be called Backup. The hostname is MyMac. The old MAC address is 00:f9:e8:d7:c6:b5 and the new MAC address 00:1a:2b:3c:4f:56.

  1. Start the Terminal Application

  2. Get the current MAC address using
    ifconfig en0 | grep ether

  3. Get the old MAC address by using
    cd /Volumes/Backup/Backups.backupdb
    xattr -p com.apple.backupd.BackupMachineAddress MyMac

  4. Disable Time Machine in System Preferences

  5. Disable ACL (access control list) using
    sudo fsaclctl -p /Volumes/Backup -d

  6. Move the old MAC address file to the new MAC address by
    sudo mv .00f9e8d7c6b56 .001a2b3c4f56
    Don’t forget to change the MAC addresses to yours.

  7. Write new MAC address to backup directory using
    sudo xattr -w com.apple.backupd.BackupMachineAddress 00:1a:2b:3c:4f:56 Backups.backupdb/MyMac
    Again, don’t forget to change the MAC addresse to yours.

  8. Move newly created backups into old directory, by
    sudo mv MyMac\ 2/* MyMac/
    The last command will result in a (harmless) error, which can be ignored. You can now delete the old directory ‘MyMac 2’ in the Finder.

  9. Re-enable ACL, using
    sudo fsaclctl -p /Volumes/Backup -e

  10. Eject and unplug the Backup disk

  11. Re-Plug the Backup disk

  12. Re-Start Time Machine (and possibly re-enable the Time Machine disk in Time Machine Preferences)

Unfortunately I have to note, that Time Machine will do a full backup after restarting. I tried to follow the comments on above site, but they all seem to be unrelated or even misleading - sorry.

Cheers,
iss