MacOS BigSur keep booting from external backup disk (made with CCC)

backupboothard drivetime-machine

My Mac is on BigSur and I am using Carbon Copy Cloner to create a one on one disk which is bootable also. I have this setup running for years now and never noticed any problems – also on BigSur it worked.

Now my Backup Drive crashed and I bought a new HDD. I have exactly build this HDD (one 1 TB partition for CCC for the one on one copy and another 1 TB partition for TimeMachine). But two major problems: The clone partition is the one that get booted after a restart – I also cannot choose another startup disk from system preferences since I only can see the actual booted one. So when I had booted with system SSD only this disk is shown and when I booted from the backup disk only this ons is shown. But the mac should boot from the internal disk by default, what could happened here?

The Drive was always plugged in in a Thunderbolt 3 Dock. I also recently switched to an eGPU (Razer Core X Chroma) which now operates as my dock where the HDD is attached. But I think the problem occurred since the new replacement disk. Also when I plug in that drive directly on my macbook this drive get booted on restart.

Another issue is that the TimeMachine partition of the disk get mountet sporadically and is making intense work but not running a time machine backup. I tried to disable the volume on spotlight which presents an error (time machine backup cannot be excluded since they are always excluded – something like that) but disabled it by command line with sudo mdutil -i off "/Volumes/TimeMachine". Now I think its better…

Maybe you have an idea.

Thanks!

— Update

The regular automatic TimeMachine backup is disabled – I have an own task that runs every hour that mounts the volume, do the TM backup and unmount it. That also worked for years now.

Best Answer

Maybe solved by reformatting the partitions to Mac OS journaled instead of apfs. Even when these programs also connect to apfs. But seems good actually. Will observe that.

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MacBook – time-machine: selective file restore – I just want a few things from a TM backup that was made of another MacBook

When you click the time machine icon in the menu bar, hold the option key. The menu will change to "Browse other time machine backups", and you should be able to access the old machine's backup in that manner.

Cannot use Disk Utility to create partition from free space on external USB drive

I think Disk Utility misses a proper EFI partition at the beginning of the disk.

If you don't want to completely erase the drive you should be successful following the steps below:

Open Terminal and enter the following to get an overview:
```
diskutil list
```
The 3 TB disk is your external disk. In the next steps I assume the disk identifier of your external disk is disk1
Get the block size of the external disk:
```
diskutil info disk1 | grep "Device Block Size"
```
In the next steps I assume that the Device Block Size is 512 bytes. If you get another block size (i.e. 4096 bytes) leave a comment.

Get the partition table of the external disk:

sudo gpt -r show /dev/disk1

The result is similar to the output below (your sizes are different though):

       start        size  index  contents
           0           1         PMBR
           1           1         Pri GPT header
           2          32         Pri GPT table
          34      262144      1  GPT part - E3C9E316-0B5C-4DB8-817D-F92DF00215AE
      262178        2014         
      264192  2244603904      2  GPT part - EBD0A0A2-B9E5-4433-87C0-68B6B72699C7
  2244868096  2048002015         
  4292870111          32         Sec GPT table
  4292870143           1         Sec GPT header

Unmount the external disk:
```
diskutil umountDisk /dev/disk1
```

Now add a third partition with

sudo gpt add -b 2244870110 -i 3 -s 1000000000 -t 48465300-0000-11AA-AA11-00306543ECAC disk1

I left some unallocated space (2014 blocks) between partition 2 and 3.

The resulting partition table looks like this then:

       start        size  index  contents
           0           1         PMBR
           1           1         Pri GPT header
           2          32         Pri GPT table
          34      262144      1  GPT part - E3C9E316-0B5C-4DB8-817D-F92DF00215AE
      262178        2014         
      264192  2244603904      2  GPT part - EBD0A0A2-B9E5-4433-87C0-68B6B72699C7
  2244868096        2014         
  2244870110  1000000000      3  GPT part - 48465300-0000-11AA-AA11-00306543ECAC
  3244870110  1048000001         
  4292870111          32         Sec GPT table
  4292870143           1         Sec GPT header

You should choose a bigger size than 1000000000 blocks. The number of blocks has to be dividable through 8. The max size in my case would have been 2048000000 (1000000000 + 1048000001).

Now format the new partition with a file system and name the volume (in the example below Backup):
```
sudo newfs_hfs -J -v "Backup" /dev/disk1s3
```

Mount the volume and verify it:

diskutil mount /dev/disk1s3
diskutil verifyVolume /dev/disk1s3

Best Answer

Related Solutions

MacBook – time-machine: selective file restore – I just want a few things from a TM backup that was made of another MacBook

Cannot use Disk Utility to create partition from free space on external USB drive

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