I am trying to fix my hard drive so that it can be formatted as APFS. Another Stack Exchange post suggests I must do the following:

  • Full clone of internal drive to external drive using SuperDuper!
  • Reboot from external drive
  • Reformat internal drive as APFS
  • Full clone of external drive to internal drive using SuperDuper!
  • Reboot from internal drive

My question is:

Why do I have to clone the internal drive to an external drive and then reboot from the external drive? What does this accomplish?

I then have to reformat the internal drive as APFS, will this somehow be more possible once I have rebooted from the external (yet cloned internal) drive?

Why is it more possible to format the internal drive as APFS once it is cloned to an external drive? And, when they say "reformat the internal drive as APFS", do they mean the clone of the internal drive that now resides on the external drive, or the actual internal drive that was left behind when the original internal was sent to the external?

  • Whoa! That accepted answer is incorrect. If you clone a drive, format it APFS, then clone it back it won't be APFS, it will be the format you originally cloned.
    – Allan
    Feb 7, 2020 at 17:16
  • @Allan - idk about SD, but CCC doesn't change the format of the partition you're cloning to - that was how I got rid of APFS [for a while] during the Sierras, to mitigate some of the worst of the TM local backup issues.
    – Tetsujin
    Feb 7, 2020 at 18:28
  • I've avoided those products, @Tetsujin because for me, they created more problems than they've solved. That must be an option in CCC because if you're not restoring the original filesystem, it's technically not a clone, it's a copy.
    – Allan
    Feb 7, 2020 at 18:32
  • @Allan - I've used CCC for a decade at least, without a single issue, ever. Personally I avoid command line because of its propensity for typonese & the disasters that causes. Horses for courses.
    – Tetsujin
    Feb 7, 2020 at 18:58
  • @Allan, I’ve personally used super duper!, and it converts the format from MacOS Journaled to APFS! Jul 12, 2021 at 15:37

1 Answer 1


Why do I have to clone the internal drive to an external drive and then reboot from the external drive? What does this accomplish?

Technically, it allows you to re-partition and format your internal drive as APFS because you can't be mounted to the drive/partition you want to modify. Booting from the external drive allows you to modify the internal drive.

Realistically speaking this is not necessary because...

  • The install of Mojave/Catalina will auto convert your SSD from JHFS+ to APFS "on the fly" during the install process

  • You can accomplish the exact same thing by simply booting from Recovery ⌘ CommandR or the USB installer of Mojave/Catalina (I prefer this method).

In terms of backing up your drive, having a clone of your drive isn't a bad thing, but Time Machine will get the job done better.

As a side note... you don't need SuperDuper or CCC (Carbon Copy Cloner). You can use the built in command dd

$ dd if=diskX of=diskY bs=1M

Where diskX = your source (internal) disk and diskY = the target (external) disk. This command will do the exact same thing as those programs.

  • Re the side note: dd doesn't do the "exact same thing as those programs". Both of them copy files (using rsync I think) rather than block copy and both omit various directories as suggested by apple (according to them). See for example CCC Knowlege Base article Some files and folders are automatically excluded from a backup task
    – lx07
    Feb 7, 2020 at 18:50
  • @lx07 - I said "accomplish the same thing" not "dd does the exact same thing" It's not even in the same context! Read Again! If they make a copy, then they're not clones. They're making copies which is misleading to begin with. That said, you don't need SD or CCC to make a copy of your internal drive to then boot from the copy. If you want to do this, you can use dd for free instead of 3rd party software that have a cost.
    – Allan
    Feb 7, 2020 at 19:21
  • SuperDuper converts the disk to apfs. Dd takes a binary backup that doesn’t change the format. Jul 12, 2021 at 15:38

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