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With the release of macOS Big Sur, I am contemplating the following plan and wanted to get some advise on any risks or if this plan will even work or not. My current setup is:

  1. macOS Catalina as the primary OS - This on an APFS container.
  2. Blank Placeholder for macOS Big Sur - This is also an APFS container.
  3. Bootcamp Partition for Windows 10.

I plan to install macOS Big Sur on the blank placeholder above; know that it is a separate container and not a new volume on the same container as the primary OS.

I have a lot of customizations on macOS Catalina and will not be able to do a clean install, migrate all apps, change all settings and migrate all customizations in one day. Allowing me to choose which OS I want to boot into will allow me to take it slowly.

When the day comes that I no longer need macOS Catalina all I need to do is delete the container and resize the macOS Big Sur container to take up all the space that's left. Will this -

  1. Cause any issues with iCloud Music and iCloud Photo libraries as I will use them on both macOS Catalina and macOS Big Sur?
  2. Jeopardize my Bootcamp partition in any way?
  3. Allow me to reclaim the space used by macOS Catalina currently so when I remove it I can allocate that space to macOS Big Sur?
  4. Any other issues?

Any advise is welcome and appreciated.

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  1. Cause any issues with iCloud Music and iCloud Photo libraries as I will use them on both macOS Catalina and macOS Big Sur?

    No.

  2. Jeopardize my Bootcamp partition in any way?

    No.

  3. Allow me to reclaim the space used by macOS Catalina currently so when I remove it I can allocate that space to macOS Big Sur?

    No.

    I would suggest one of the following two alternatives.

    • Use the Disk Utility to add a new APFS volume in the same APFS container partition as Catalina, then install Big Sur to this new APFS volume. Later, you can use the Big Sur Disk Utility to delete the Catalina volume group.
    • Boot to Catalina macOS Recovery. Use the Disk Utility to create a new APFS container partition. Enter the same name use by current Catalina. Next, use the Disk Utility to restore (replicate) Catalina to this new APFS container partition. Quit the Disk Utility and then choose →Startup Disk… from the menu bar. Choose to restart from the replicated Catalina. This would be the one that is not initially highlighted. Use the Disk Utility to erase the APFS container partition with the original Catalina. Enter a name for the new APFS volume where Big Sur will be installed. Next, quit the Disk Utility and install Big Sur to the new APFS volume you just created. If necessary, first download Big Sur from the App Store. Later, you can remove the APFS container partition with the replicated Catalina and merge the space back into the APFS container partition with Big Sur.

  4. Any other issues?

    No.

    However, user user3439894 has suggested the following popup message could be an issue. This popup may occur when booting Mojave on a Mac with Mojave and Big Sur installed in either the same or different APFS containers.

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  • You should probably take a look at WARNING: Do not install Big Sur on the same APFS container as previous versions of MacOS. It was back during the beta releases, however, it still may be an issue with the GM release.
    – user3439894
    Nov 14, 2020 at 23:08
  • @user3439894: I have Mojave and the just released Big Sur installed in the same APFS container on the internal SSD of a 2018 mac mini. I also have Mojave installed in a different APFS container on a thunderbolt 3 external SSD which is plugged into the same 2018 mac mini. The problem with updates, which occurred with a beta Big Sur release, does apply to the current Big Sur release. However, when booted to either Mojave, this popup occurs.
    – David Anderson
    Nov 14, 2020 at 23:58
  • While Apple felt a message was needed, a user should always assume a new version of an operating systems would offer features that are not supported in previous releases. This was true when I had a Mojave and Catalina dual boot, even though there was no pop message. For example, a verify of the APFS container under Mojave would show errors, but not when done under Catalina. So far, I have not had any problems with the current Mojave and Big Sur dual boot.
    – David Anderson
    Nov 15, 2020 at 0:08
  • I could put all macOSes in separate APFS containers, but as I already stated the pop message occurs with booting to the Mojave which is already in a separate APFS container on the thunderbolt 3 external SSD.
    – David Anderson
    Nov 15, 2020 at 0:10
  • So, the "No" answer to "4. Any other issues?" is not necessarily a true statement then.
    – user3439894
    Nov 15, 2020 at 0:10

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