Triple Boot Big Sur, Mojave, and Windows 10

Question

Level 1

8 points

Triple Boot Big Sur, Mojave, and Windows 10

Right now I’m dual booting Mojave and Big Sur. Long ago I decided I wanted to boot Windows 10 on my Mac, but after I made the partition, there was some sort of error and I gave up. Now I’d like to try to boot Windows again. However, I currently have 3 partitions on my Mac: Big Sur, Mojave, and one called “BOOTCAMP”, which I assume is the partition I made before the error long ago. When I open up Boot Camp Assistant, it says I have to delete the Windows partition. If I click Restore, will my Mac still have my Big Sur and Mojave partitions and all of the data on each of them? There are very important files on both partitions. Thanks in advance.

iMac Line (2012 and Later)

Posted on May 5, 2021 4:18 PM

Reply

Answer 1

Top-ranking reply

Loner T

Level 9

59,536 points

May 6, 2021 2:15 PM in response to Joe_Marsh

OSXRESERVED is a partition used to build a W10 installer and boot from. BOOTCAMP is your designated Windows install destination.

If you run BC Assistant, it should offer to cleanup and remove both these partitions, which will allow you to re-run BCA and start the process again. Be aware that Big Sur EFI has many issues with Windows.

Reply

Answer 2

Loner T

Level 9

59,536 points

May 5, 2021 5:17 PM in response to Joe_Marsh

From macOS Terminal, post the output of

diskutil list

Normally, under APFS, you can install more than one macOS version within the same APFS Container, on separate APFS volumes (not partitons). See Installing macOS on a separate APFS volume - Apple Support for reference. There are some caveats to this approach, but in general it does work.

However, if you did not use this method, and manually created partitions, then each APFS Container will use an underlying physical partition. If such partitioning was done after a failed attempt at installing Windows via Bootcamp, you may have leftover partition(s) from such an attempt. This disk state does not support installing Windows via Bootcamp anymore.

The requested output should show the exact state, before any alternatives can be further explored.

Reply

Answer 3

Joe_Marsh Author

Level 1

8 points

May 6, 2021 4:10 AM in response to Loner T

Thanks for the response. I’m a bit confused, but I believe I understand what you are saying. I dual booted Big Sur and Catalina last summer during the quarantine, long after my failed attempt to boot Windows as well. It was a while ago, but if I remember correctly, I did it by making another volume for Mojave that shares its space with my main volume, which sounds similar to the page you linked me. Then I had a Mojave installer, and was able to select the volume on which it would be installed. The only other part of the process I remember is that I needed to use a USB stick to download it. If that is the process you were referring to, does that mean I can safely restore the Boot Camp partition without wiping my Big Sur and Mojave volumes? Does that mean I can retry booting Windows once I’m done? Thanks in advance.

Edit: I’ll run that command too once I have the chance later today.

Reply

Answer 4

Joe_Marsh Author

Level 1

8 points

May 6, 2021 12:08 PM in response to Loner T

Here is the output. The exact names of my volumes/partitions are "DO NOT DELETE Mojave Disk" (I share this computer), "OSXRESERVED" (Which I assume to be the Big Sur one), and "BOOTCAMP". Thanks.

/dev/disk0 (internal, physical):

#: TYPE NAME SIZE IDENTIFIER

0: GUID_partition_scheme *24.0 GB disk0

1: EFI ⁨EFI⁩ 314.6 MB disk0s1

2: Apple_APFS ⁨Container disk2⁩ 23.7 GB disk0s2

/dev/disk1 (internal, physical):

#: TYPE NAME SIZE IDENTIFIER

0: GUID_partition_scheme *1.0 TB disk1

1: EFI ⁨EFI⁩ 209.7 MB disk1s1

2: Apple_APFS ⁨Container disk2⁩ 857.3 GB disk1s2

3: Microsoft Basic Data ⁨OSXRESERVED⁩ 10.0 GB disk1s3

4: Microsoft Basic Data ⁨BOOTCAMP⁩ 132.7 GB disk1s4

/dev/disk2 (synthesized):

#: TYPE NAME SIZE IDENTIFIER

0: APFS Container Scheme - +881.0 GB disk2

Physical Stores disk0s2, disk1s2

1: APFS Volume ⁨Macintosh HD - Data⁩ 271.4 GB disk2s1

2: APFS Volume ⁨Preboot⁩ 340.4 MB disk2s2

3: APFS Volume ⁨Recovery⁩ 1.1 GB disk2s3

4: APFS Volume ⁨VM⁩ 3.2 GB disk2s4

5: APFS Volume ⁨Macintosh HD⁩ 15.1 GB disk2s5

6: APFS Snapshot ⁨com.apple.os.update-...⁩ 15.1 GB disk2s5s1

7: APFS Volume ⁨DO NOT DELETE Mojave...⁩ 159.5 GB disk2s6

Reply

Answer 5

Joe_Marsh Author

Level 1

8 points

May 6, 2021 2:29 PM in response to Loner T

Thank you so much! I always knew there was something up with the OSXRESERVED partition, as it says Macintosh when I boot back into Big Sur. You've already answered my main question, but if you don't mind, what exactly is the Big Sur "EFI", and what issues does it have? Even if you can't answer, I appreciate your help. Thank you and have a great day.

Reply

Answer 6

Loner T

Level 9

59,536 points

May 6, 2021 4:09 PM in response to Joe_Marsh

EFI is a firmware layer on your Mac that is between the hardware and the OS. Versions of firmware are release for Macs, bundled with macOS releases and can also be updated otherwise, if needed. The EFI firmware versions of macOS Catalina and older are friendlier to Windows than the version that comes with Big Sur, presumably to support Apple Silicon. macOS Catalina and Mojave have fewer issues with Windows than macOS Big Sur and macOS High Sierra.

Reply

Answer 7

Loner T

Level 9

59,536 points

May 6, 2021 6:58 AM in response to Joe_Marsh

Joe_Marsh wrote:

Edit: I’ll run that command too once I have the chance later today.

Once you post the output, we can decide the next step(s).

Reply

Triple Boot Big Sur, Mojave, and Windows 10

Similar questions