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cMP5,1 and Apple BOOTCAMP assistant for creating Windows 10 partition

startergo

macrumors 68030
Original poster
Sep 20, 2018
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Here is a little study on the official BOOTCAMP for the cMP5,1. It may be valid for other Macs, but it is not guaranteed.
As you may know BOOTCAMP assistant throws this message, when you try to open it in an APFS formatted drive (Mojave and Catalina):
1589107528985.png

I modified the BOOTCAMP Info.plist from a High Sierra drive (attached below along with the Bootcamp app) so that you can install Windows 10 on an HFS+ formatted drive alongside another HFS+ drive. This is how it creates the partitions. I renamed the Windows partition with gdisk:
Code:
gdisk /dev/disk4
GPT fdisk (gdisk) version 1.0.4

Warning: Devices opened with shared lock will not have their
partition table automatically reloaded!
Partition table scan:
  MBR: hybrid
  BSD: not present
  APM: not present
  GPT: present

Found valid GPT with hybrid MBR; using GPT.

Command (? for help): p
Disk /dev/disk4: 488281250 sectors, 232.8 GiB
Sector size (logical): 512 bytes
Disk identifier (GUID): F149294D-B5AA-4C2C-BF5D-9B2B313CCB9A
Partition table holds up to 128 entries
Main partition table begins at sector 2 and ends at sector 33
First usable sector is 34, last usable sector is 488281216
Partitions will be aligned on 8-sector boundaries
Total free space is 264791 sectors (129.3 MiB)

Number  Start (sector)    End (sector)  Size       Code  Name
   1              40          409639   200.0 MiB   EF00  EFI System Partition
   2          409640       243878447   116.1 GiB   AF00
   3       244142080       488280063   116.4 GiB   0700  Win10Legacy

As you can see it creates
MBR: hybrid
partitions on the GPT drive. Windows treats such partitions as MBR even though it is installed on a GPT drive. For more information please read the excellent Rod Smith's guide:
http://www.rodsbooks.com/gdisk/hybrid.html


1589108578905.png

It may work on a single partition as well but it will install in UEFI Mode (untested) because as a single partition it does not create the same type of partitions:

Code:
 gdisk /dev/disk2
GPT fdisk (gdisk) version 1.0.4

Warning: Devices opened with shared lock will not have their
partition table automatically reloaded!
Partition table scan:
  MBR: protective
  BSD: not present
  APM: not present
  GPT: present

Found valid GPT with protective MBR; using GPT.

Command (? for help): p
Disk /dev/disk2: 488397168 sectors, 232.9 GiB
Sector size (logical): 512 bytes
Disk identifier (GUID): 803ED14A-61F2-4BE1-9B33-46F5B2159BA6
Partition table holds up to 128 entries
Main partition table begins at sector 2 and ends at sector 33
First usable sector is 34, last usable sector is 488397134
Partitions will be aligned on 8-sector boundaries
Total free space is 2349 sectors (1.1 MiB)

Number  Start (sector)    End (sector)  Size       Code  Name
   1              40          409639   200.0 MiB   EF00  EFI System Partition
   2          411648       488396799   232.7 GiB   0700
As compared to the case where we created a second partition on an HFS+ drive alongside the regular HFS+ partition this is not a hybrid MBR drive. Booting from Windows in UEFI drive may create ROM havoc as it may write multiple certificates in the NVRAM. It is recommended to use Windows in UEFI Mode only through OpenCore booting. Please see the OpenCore thread for details.
Another advantage of creating a Windows 10 BOOTCAMP partition alongside the HFS+ partition is that you can boot to Windows from the Startup disk.
Unfortunately it does not work on an APFS drives as it can't find free space on them:
1589111739065.png

The bootcamp assistant from APFS formatted drives in Mojave or Catalina has a different binary inside. It is not a matter of only modifying the Info.plist. No matter how you modify the plist you will get:
1589107528985.png

The binary has to be patched to support cMP5,1:
1589112128821.png


If you want to create your own BOOTCAMP assistant You need to copy it from the
/Application/Utilities
on an HS HFS+ drive, modify the plist as in the sample and:

OPTIONAL: Restore original permissions (recommended).
For security reasons, it is recommended to restore the original permissions within the Boot Camp Assistantapplication package. In FinderApplicationsUtilitiesTerminal, enter the following commands as necessary to remove "write" permissions for "group" and "other" users:

sudo chmod go-w /path/to/your/Boot\ Camp\ Assistant.app/Contents/Info.plist
sudo chmod go-w /path/to/your/Boot\ Camp\ Assistant.app/Contents

Or, right-click on the Boot Camp Assistant.app file → Show Package Contents, then within the Contentsfolder, right-click on the Info.plist file → Get Info. Then click to unlock the icon in the bottom right corner (and enter your password if prompted), then set the privileges for everything other than "system" to "Read only". Repeat for the Contents folder itself.

Code-sign the edited application package (if necessary).
Some versions of macOS will require the Boot Camp Assistant application package to be code-signed in order to run it. In FinderApplicationsUtilitiesTerminal, enter one of the following commands to sign it ad-hoc(without an identity):

sudo codesign --force --sign - /path/to/your/Boot\ Camp\ Assistant.app
  • If that doesn't work, then for later versions of macOS, nested content must be signed as well, by specifying the --deep option:
sudo codesign --force --sign - /path/to/your/Boot\ Camp\ Assistant.app --deep
NOTE: If Xcode Command Line Tools are not already installed, the above commands may prompt to do so; afterward, the above commands may need to be run again.

I used this guide partially:
First you need to create the USB installer and leave it plugged in during BOOTCAMP creation. You will not need it to install Windows as it will be installed through VirtualBox and a Windows iso image attached.
1589114630166.png


You may open terminal and enter root
Code:
sudo -s
To prevent reboot after successful BOOTCAMP partition creation.
Once you create the BOOTCAMP partition just use this guide for installing Windows:

But when creating the Virtual Machine make sure you DO NOT ENABLE EFI:
1589113875337.png

On the first boot all you have to do from the Windows Partitioning wizard is to format the BOOTCAMP drive as it will convert it from FAT32 to NTFS. Later you can rename it with gdisk.
You can use the bootcamp drivers from the earlier created USB to install the drivers once in Windows. After you install the drivers you may uninstall the bootcamp 5,1 and reinstall the one from iMacPro1,1 to get all the drives to appear in the Windows Bootcamp manager. Use commands:
Code:
msiexec /x path_to_the/BootCamp/Drivers/Apple/BootCamp.msi
to uninstall bootcamp 5.1. You need to select BootCamp.msi you used to install it.
To install the iMacPro BootCamp.msi use brigadier to download it. Open CMD (as administrator just in case) and browse to the brigadier folder and use:
Code:
brigadier.exe -m iMacPro1,1

To install the new 6.1 Bootcamp.msi
Code:
msiexec /i path_to_the/BootCamp/Drivers/Apple/BootCamp.msi

You may be able to install Hybrid partitions on an APFS drive using gdisk, but I haven't tested it.
Create a BOOTCAMP Partition on that drive:
1589116696912.png

And use gdisk:


Code:
root@G5s-Mac-Pro ~ # gdisk /dev/disk1
GPT fdisk (gdisk) version 1.0.4

Warning: Devices opened with shared lock will not have their
partition table automatically reloaded!
Partition table scan:
  MBR: protective
  BSD: not present
  APM: not present
  GPT: present

Found valid GPT with protective MBR; using GPT.

Command (? for help): r

Recovery/transformation command (? for help): p
Disk /dev/disk1: 1000215216 sectors, 476.9 GiB
Sector size (logical): 512 bytes
Disk identifier (GUID): DF8BA5A4-2A3A-4A1B-9F1F-AA6A6332D9A5
Partition table holds up to 128 entries
Main partition table begins at sector 2 and ends at sector 33
First usable sector is 34, last usable sector is 1000215182
Partitions will be aligned on 8-sector boundaries
Total free space is 3213 sectors (1.6 MiB)

Number  Start (sector)    End (sector)  Size       Code  Name
   1              40          409639   200.0 MiB   EF00  EFI System Partition
   2          409640       707245575   337.0 GiB   AF0A  CATALINA
   3       707246080      1000212479   139.7 GiB   0700

Recovery/transformation command (? for help): h

WARNING! Hybrid MBRs are flaky and dangerous! If you decide not to use one,
just hit the Enter key at the below prompt and your MBR partition table will
be untouched.

Type from one to three GPT partition numbers, separated by spaces, to be
added to the hybrid MBR, in sequence: 1 2 3
Place EFI GPT (0xEE) partition first in MBR (good for GRUB)? (Y/N): n

Creating entry for GPT partition #1 (MBR partition #1)
Enter an MBR hex code (default EF):
Set the bootable flag? (Y/N): n

Creating entry for GPT partition #2 (MBR partition #2)
Enter an MBR hex code (default AF):
Set the bootable flag? (Y/N): n

Creating entry for GPT partition #3 (MBR partition #3)
Enter an MBR hex code (default 07):
Set the bootable flag? (Y/N): n

Recovery/transformation command (? for help): o

Disk size is 1000215216 sectors (476.9 GiB)
MBR disk identifier: 0x0A332465
MBR partitions:

Number  Boot  Start Sector   End Sector   Status      Code
   1                    40       409639   primary     0xEF
   2                409640    707245575   primary     0xAF
   3             707246080   1000212479   primary     0x07
   4                     1           39   primary     0xEE

Recovery/transformation command (? for help):

or:

Code:
root@G5s-Mac-Pro ~ # gdisk /dev/disk1
GPT fdisk (gdisk) version 1.0.4

Warning: Devices opened with shared lock will not have their
partition table automatically reloaded!
Partition table scan:
  MBR: protective
  BSD: not present
  APM: not present
  GPT: present

Found valid GPT with protective MBR; using GPT.

Command (? for help): r

Recovery/transformation command (? for help): p
Disk /dev/disk1: 1000215216 sectors, 476.9 GiB
Sector size (logical): 512 bytes
Disk identifier (GUID): DF8BA5A4-2A3A-4A1B-9F1F-AA6A6332D9A5
Partition table holds up to 128 entries
Main partition table begins at sector 2 and ends at sector 33
First usable sector is 34, last usable sector is 1000215182
Partitions will be aligned on 8-sector boundaries
Total free space is 3213 sectors (1.6 MiB)

Number  Start (sector)    End (sector)  Size       Code  Name
   1              40          409639   200.0 MiB   EF00  EFI System Partition
   2          409640       707245575   337.0 GiB   AF0A  CATALINA
   3       707246080      1000212479   139.7 GiB   0700

Recovery/transformation command (? for help): h

WARNING! Hybrid MBRs are flaky and dangerous! If you decide not to use one,
just hit the Enter key at the below prompt and your MBR partition table will
be untouched.

Type from one to three GPT partition numbers, separated by spaces, to be
added to the hybrid MBR, in sequence: 1 2 3
Place EFI GPT (0xEE) partition first in MBR (good for GRUB)? (Y/N): Y

Creating entry for GPT partition #1 (MBR partition #2)
Enter an MBR hex code (default EF):
Set the bootable flag? (Y/N): n

Creating entry for GPT partition #2 (MBR partition #3)
Enter an MBR hex code (default AF):
Set the bootable flag? (Y/N): n

Creating entry for GPT partition #3 (MBR partition #4)
Enter an MBR hex code (default 07):
Set the bootable flag? (Y/N): n

Recovery/transformation command (? for help): o

Disk size is 1000215216 sectors (476.9 GiB)
MBR disk identifier: 0x0A332465
MBR partitions:

Number  Boot  Start Sector   End Sector   Status      Code
   1                     1           39   primary     0xEE
   2                    40       409639   primary     0xEF
   3                409640    707245575   primary     0xAF
   4             707246080   1000212479   primary     0x07

Recovery/transformation command (? for help):
 

Attachments

  • Boot Camp Assistant.zip
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  • Info.plist.zip
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Last edited:

startergo

macrumors 68030
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As of continuation of testing I have converted the APFS drive to partitions with hybrid MBR and installed BOOTCAMP through VirtualBox in legacy mode on the same drive using the below conversion and later renamed the partition:
Started from creating FAT32 partition
1589135187799.png

Code:
sudo gdisk /dev/disk1
Password:
GPT fdisk (gdisk) version 1.0.4

Warning: Devices opened with shared lock will not have their
partition table automatically reloaded!
Partition table scan:
  MBR: protective
  BSD: not present
  APM: not present
  GPT: present

Found valid GPT with protective MBR; using GPT.

Command (? for help): r

Recovery/transformation command (? for help): p
Disk /dev/disk1: 1000215216 sectors, 476.9 GiB
Sector size (logical): 512 bytes
Disk identifier (GUID): DF8BA5A4-2A3A-4A1B-9F1F-AA6A6332D9A5
Partition table holds up to 128 entries
Main partition table begins at sector 2 and ends at sector 33
First usable sector is 34, last usable sector is 1000215182
Partitions will be aligned on 8-sector boundaries
Total free space is 3213 sectors (1.6 MiB)

Number  Start (sector)    End (sector)  Size       Code  Name
   1              40          409639   200.0 MiB   EF00  EFI System Partition
   2          409640       707245575   337.0 GiB   AF0A  CATALINA
   3       707246080      1000212479   139.7 GiB   0700

Recovery/transformation command (? for help): h

WARNING! Hybrid MBRs are flaky and dangerous! If you decide not to use one,
just hit the Enter key at the below prompt and your MBR partition table will
be untouched.

Type from one to three GPT partition numbers, separated by spaces, to be
added to the hybrid MBR, in sequence: 1 2 3
Place EFI GPT (0xEE) partition first in MBR (good for GRUB)? (Y/N): n

Creating entry for GPT partition #1 (MBR partition #1)
Enter an MBR hex code (default EF):
Set the bootable flag? (Y/N): n

Creating entry for GPT partition #2 (MBR partition #2)
Enter an MBR hex code (default AF):
Set the bootable flag? (Y/N): n

Creating entry for GPT partition #3 (MBR partition #3)
Enter an MBR hex code (default 07):
Set the bootable flag? (Y/N): n

Recovery/transformation command (? for help): o

Disk size is 1000215216 sectors (476.9 GiB)
MBR disk identifier: 0x0A332465
MBR partitions:

Number  Boot  Start Sector   End Sector   Status      Code
   1                    40       409639   primary     0xEF
   2                409640    707245575   primary     0xAF
   3             707246080   1000212479   primary     0x07
   4                     1           39   primary     0xEE

Recovery/transformation command (? for help): w

Final checks complete. About to write GPT data. THIS WILL OVERWRITE EXISTING
PARTITIONS!!

Do you want to proceed? (Y/N): y
OK; writing new GUID partition table (GPT) to /dev/disk1.
Warning: Devices opened with shared lock will not have their
partition table automatically reloaded!
Warning: The kernel may continue to use old or deleted partitions.
You should reboot or remove the drive.
The operation has completed successfully.


% sudo gdisk /dev/disk1
GPT fdisk (gdisk) version 1.0.4

Partition table scan:
  MBR: hybrid
  BSD: not present
  APM: not present
  GPT: present

Found valid GPT with hybrid MBR; using GPT.

Command (? for help): p
Disk /dev/disk1: 1000215216 sectors, 476.9 GiB
Sector size (logical): 512 bytes
Disk identifier (GUID): DF8BA5A4-2A3A-4A1B-9F1F-AA6A6332D9A5
Partition table holds up to 128 entries
Main partition table begins at sector 2 and ends at sector 33
First usable sector is 34, last usable sector is 1000215182
Partitions will be aligned on 8-sector boundaries
Total free space is 3213 sectors (1.6 MiB)

Number  Start (sector)    End (sector)  Size       Code  Name
   1              40          409639   200.0 MiB   EF00  EFI System Partition
   2          409640       707245575   337.0 GiB   AF0A  CATALINA
   3       707246080      1000212479   139.7 GiB   0700

Command (? for help): c
Partition number (1-3): 3
Enter name: WIN10APFSL

Command (? for help): w

Final checks complete. About to write GPT data. THIS WILL OVERWRITE EXISTING
PARTITIONS!!

Do you want to proceed? (Y/N): y
OK; writing new GUID partition table (GPT) to /dev/disk1.
Warning: The kernel may continue to use old or deleted partitions.
You should reboot or remove the drive.
The operation has completed successfully.
g5@G5s-Mac-Pro ~ % sudo gdisk /dev/disk1
GPT fdisk (gdisk) version 1.0.4

Partition table scan:
  MBR: hybrid
  BSD: not present
  APM: not present
  GPT: present

Found valid GPT with hybrid MBR; using GPT.

Command (? for help): p
Disk /dev/disk1: 1000215216 sectors, 476.9 GiB
Sector size (logical): 512 bytes
Disk identifier (GUID): DF8BA5A4-2A3A-4A1B-9F1F-AA6A6332D9A5
Partition table holds up to 128 entries
Main partition table begins at sector 2 and ends at sector 33
First usable sector is 34, last usable sector is 1000215182
Partitions will be aligned on 8-sector boundaries
Total free space is 3213 sectors (1.6 MiB)

Number  Start (sector)    End (sector)  Size       Code  Name
   1              40          409639   200.0 MiB   EF00  EFI System Partition
   2          409640       707245575   337.0 GiB   AF0A  CATALINA
   3       707246080      1000212479   139.7 GiB   0700  WIN10APFSL

Command (? for help):
Followed the same procedure to install Windows through VirtualBox as described in the first post.
Booted to Windows and installed 5,1--> 6.1 (iMacPro1,1) drivers as described in the first post. Booted to Catalina to make sure the drive did not corrupt.
Everything works as designed.
Some observations:
I have 2 identical RX-480. One without EFI and one with MVC EFI attached to separate screens.
When I first boot, the screen with the EFI video card shows the bootpicker. As soon as I select Legacy Windows the Windows progress bar switches to the regular GOP videocard and the boot screen remains frozen on the other card.
On one of the Windows installs after booting to Windows, it found automatically the video drivers and I saw output to both screens. On my second install after Windows automatic driver installation, the screen attached to the EFI card just turned black, but could not produce output. Legacy Windows does not like EFI videocards. Anyway I am sure if I remove the GOP card Windows will switch the output to the EFI card, but I am just letting you know as your mileage may vary. You will need the boot screen on first boot and then you can select the Windows partition and click cntrl+enter (blessing the boot partition from the boot picker). Before the next start you may replace the EFI card with the non EFI card.
The main goal of this post is to confirm that Windows 10 can be installed "the Apple way" with modified Bootcamp assistant on the HFS+ drive formatted as GPT, or on APFS drive formatted as GPT using gdisk to convert partitions to Hybrid MBR knowing already the formatting process of the Bootcamp Assistant.

IMPORTANT:
Before making any changes do a BACKUP of the partitions involved in partitioning/resizing.
Save a copy of the disk layout before/after repartitioning for troubleshooting REDO purposes!
 
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startergo

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PART 3: attempt to make the Bootcamp partition bootable in both MBR and UEFI Mode.
1. Changed the Original Apple BOOTCAMP installation VirtualBox machine to extended features: Enable EFI.
2. Attached the Windows ISO to the CD-ROM
3.Booted from the CD-ROM.
4. SHFT+F10 opens command prompt.
Unfortunately the EFI disk Created by Apple is not seen from the WINPE therefore no chance installing the Boot Loader in the EFI partition on the Apple Hybrid MBR type partitioning.

Whenever you modify partition using gdisk make a note of the partition layout and a data backup (if you have important files on the drive) by using:
Code:
sudo fdisk /dev/disk6 >> Geometry.txt  && sudo gpt -r show disk6 >> Geometry.txt
Code:
Disk: /dev/disk6    geometry: 30394/255/63 [488281250 sectors]
Signature: 0xAA55
         Starting       Ending
#: id  cyl  hd sec -  cyl  hd sec [     start -       size]
------------------------------------------------------------------------
1: EE 1023 254  63 - 1023 254  63 [         1 -     409639] <Unknown ID>
2: AF 1023 254  63 - 1023 254  63 [    409640 -  243468808] HFS+     
*3: 07 1023 254  63 - 1023 254  63 [ 244142080 -  244137984] HPFS/QNX/AUX
4: 00    0   0   0 -    0   0   0 [         0 -          0] unused   
      start       size  index  contents
          0          1         MBR
          1          1         Pri GPT header
          2         32         Pri GPT table
         34          6       
         40     409600      1  GPT part - C12A7328-F81F-11D2-BA4B-00A0C93EC93B
     409640  243468808      2  GPT part - 48465300-0000-11AA-AA11-00306543ECAC
  243878448     263632       
  244142080  244137984      3  GPT part - EBD0A0A2-B9E5-4433-87C0-68B6B72699C7
  488280064       1153       
  488281217         32         Sec GPT table
  488281249          1         Sec GPT header

And then:
Code:
sudo dd if=/dev/disk6 bs=512 count=63 of=bootblockMBR.bin && hexdump -Cv bootblockMBR.bin > bootblockMBR.txt
sudo dd if=/dev/disk6 skip=409640 count=3 of=bootblockHFS.bin && hexdump -Cv bootblockHFS.bin > bootblockHFS.txt
sudo dd if=/dev/disk6 skip=244142080 count=63 of=bootblockNTFS.bin && hexdump -Cv bootblockNTFS.bin > bootblockNTFS.txt


To update the MBR partition table, a mapping of the partition types needs to be known. Below is a table of some commonly found types:

Code:
          Partition Type              MBR ID              UEFI GUID
--------------------------------------  ------  ------------------------------------
Apple Mac OS Extended (HFS+ or JHFS+)     AF    48465300-0000-11AA-AA11-00306543ECAC
Apple Boot (Recovery HD)                  AB    426F6F74-0000-11AA-AA11-00306543ECAC
Apple Core Storage                        AC    53746F72-6167-11AA-AA11-00306543ECAC
Apple File System (APFS)                  AF    7C3457EF-0000-11AA-AA11-00306543ECAC
Extensible Firmware Interface (EFI)       EE    C12A7328-F81F-11D2-BA4B-00A0C93EC93B
Linux Filesystem Data                     83    0FC63DAF-8483-4772-8E79-3D69D8477DE4
Linux Swap                                82    0657FD6D-A4AB-43C4-84E5-0933C84B4F4F
Linux Logical Volume Manager (LVM)        8E    E6D6D379-F507-44C2-A23C-238F2A3DF928
Microsoft File Attribute Table (FAT32)    0C    EBD0A0A2-B9E5-4433-87C0-68B6B72699C7
Microsoft Windows NT (NTFS) or ExFAT      07    EBD0A0A2-B9E5-4433-87C0-68B6B72699C7
Microsoft Windows Recovery Environment    27    DE94BBA4-06D1-4D40-A16A-BFD50179D6AC

You can follow these instructions to convert GPT to Hybrid GPT/MBR.
Unfortunately booting BOOTCAMP the Apple way in both UEFI and MBR mode seems impossible due to the fact that once you convert to hybrid MBR Windows does not see the EFI partition. Also of note here is whatever you convert/create as a partition scheme outside of Windows should not be altered from within Windows otherwise you will have to recreate the MBR table.
For instance you created Hybrid MBR and BOOTCAMP FAT32 partition. Then you boot the drive in the VirtualBox but instead of formatting the drive to NTFS you delete the partition. Windows will install most probably, but will also create another active system partition holding the BCD store. This already breaks the Apple scheme and you may not be able to see Windows in the Startup Disk nor will it boot from the boot picker while holding option key.
 
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startergo

macrumors 68030
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One thing to make clear about raw disk access in VirtualBox:
On every reboot the disk ID might change. You can verify that in the Disk Utility. Unfortunately the .vmdk created for raw disk access holds the original disk number. You can inspect the file with Hex Fiend:
1589723632285.png

So when you try to open that file you will in fact be opening the current disk 1 in VirtualBox.
I cannot find an absolute path for usage like the disk GUID:
Code:
sudo Sudo VBoxManage internalcommands createrawvmdk -filename "/Users/<user>/Documents/test.vmdk" -rawdisk 8A1764D4-3005-495B-8AE6-AD1211D749A8
VBoxManage: error: Cannot open the raw disk '8A1764D4-3005-495B-8AE6-AD1211D749A8': VERR_FILE_NOT_FOUND
VBoxManage: error: The raw disk vmdk file was not created
So unless there is a way to define absolute path to the VMDK pointer, which does not change upon reboot you have to delete the VM, and recreate the raw disk VMDK again
or
You can add yourself to the permissions of the VMDK file with read/write access and modify the partition id in Hex Fiend.
 
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startergo

macrumors 68030
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I have just played with the BOOTCAMP assistant in BigSur. It works for the cMP for creation of Windows 10 partition in MBR (hybrid) mode.
First I created a BigSur on an external hard drive (NVME) on MBP15,1:
1606138812022.png

Secure Boot- No security, External Boot- Allow booting from external media. I have an NVME drive attached to an envoyexpress enclosure.
Formatted the drive as APFS GPT. Installed BigSur. Attempted to install Windows, but the Bootcamp assistant complained about the existence of an external drive. Removed the NVME drive and installed it on a PCIE card inside the cMP. In Mojave issued:
Code:
sudo nvram boot-args="-no_compat_check"
Rebooted to BigSur. Started Bootcamp assistant. Prepared a USB drive and Windows iso file. Entered:
Code:
sudo -s
(Root) in terminal to prevent automatic reboot.
Created BOOTCAMP partition. Then I removed the drive and compared the partition created in Windows on my MBP15,1:
1606139499697.png

As you can see the Bootcamp assistant from BigSur in cMP created a hybrid partition (Disk0). The Bootcamp assistant in my MBP15,1 created a UEFI partition (Disk1) from within Catalina's Bootcamp Assistant.
 
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startergo

macrumors 68030
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Code:
sudo gpt -r show disk1
Password:
gpt show: disk1: Suspicious MBR at sector 0
      start       size  index  contents
          0          1         MBR
          1          1         Pri GPT header
          2         32         Pri GPT table
         34          6        
         40     409600      1  GPT part - C12A7328-F81F-11D2-BA4B-00A0C93EC93B
     409640  488281248      2  GPT part - 7C3457EF-0000-11AA-AA11-00306543ECAC
  488690888        824        
  488691712  488081408      3  GPT part - EBD0A0A2-B9E5-4433-87C0-68B6B72699C7
  976773120         15        
  976773135         32         Sec GPT table
  976773167          1         Sec GPT header
1606146571284.png


This is the new layout after creation of the Bootcamp Partition. It can be removed after consecutive run of the Bootcamp assistant:
1606146670848.png

How to convert the hybrid partition created from the Bootcamp assistant in Big Sur from MBR to UEFI Apple style:
 
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