1

after following this detailed guide I've stuck at point 5. which did not make my external 5TB HDD to boot, no "Install Windows" nor "Windows" shows in boot selection menu:

bless --folder /Volumes/WINSTALL/efi/boot --label "Install Windows"
mkdir /Volumes/WINSTALL/label
bless --folder /Volumes/WINSTALL/label --label "Windows"

Current disk configuration of iMac 2012:

  • 1TB internal HDD (currently installed Catalina, Windows 10)
  • 240GB external SSD (Thunderbolt 2: currently installed Mojave, High Sierra)
  • 5TB external HDD (USB: empty)

Target is to install Windows 10 on external Thunderbold2 240GB SSD along with the other OS installations.

diskutil list shows following configuration:

/dev/disk0 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *240.1 GB   disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:                 Apple_APFS Container disk4         117.0 GB   disk0s2
   3:       Microsoft Basic Data BOOTCAMP                87.7 GB    disk0s3
   4:                 Apple_Boot Boot OS X               134.2 MB   disk0s4
   5:                 Apple_APFS Container disk2         35.0 GB    disk0s5

/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 disk3         395.0 GB   disk1s2
   3:       Microsoft Basic Data BOOTCAMP                605.0 GB   disk1s3

/dev/disk2 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +35.0 GB    disk2
                                 Physical Store disk0s5
   1:                APFS Volume macOS-HS                14.2 GB    disk2s1
   2:                APFS Volume Preboot                 22.8 MB    disk2s2
   3:                APFS Volume Recovery                512.1 MB   disk2s3
   4:                APFS Volume VM                      2.1 GB     disk2s4

/dev/disk3 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +395.0 GB   disk3
                                 Physical Store disk1s2
   1:                APFS Volume Macintosh HD - Data     367.9 GB   disk3s1
   2:                APFS Volume Preboot                 25.6 MB    disk3s2
   3:                APFS Volume Recovery                525.8 MB   disk3s3
   4:                APFS Volume VM                      8.6 GB     disk3s4
   5:                APFS Volume Macintosh HD            11.3 GB    disk3s5

/dev/disk4 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +117.0 GB   disk4
                                 Physical Store disk0s2
   1:                APFS Volume iMextMojave             85.3 GB    disk4s1
   2:                APFS Volume Preboot                 26.1 MB    disk4s2
   3:                APFS Volume Recovery                507.5 MB   disk4s3
   4:                APFS Volume VM                      2.1 GB     disk4s4

/dev/disk5 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *5.0 TB     disk5
   1:                        EFI EFI                     209.7 MB   disk5s1
   2:                  Apple_HFS seagate                 5.0 TB     disk5s2
   3:       Microsoft Basic Data Winstall                15.9 GB    disk5s3

Because the first attempt with external 5TB HDD did not work I tried to use 240GB SSD with Bootcamp Assistant in Mojave (OS booted from that SSD) to create installation USB-stick and to create Bootcamp partition on SSD with ISO Win10 64-bit 1909 as recommended in the guide.

At point 8. I tried to assign letter "S" to EFI partition on SSD but it failed with message There is no volume specified. Please select a volume and try again. So I tried to mount the partition with command mountvol S: /S without success and when I tried to run mountvol with no arguments it did not even show EFI partitions from the other disks as an option.

Disk status in Windows Setup:

DISKPART> list disk

  Disk ###  Status         Size     Free     Dyn  Gpt
  --------  -------------  -------  -------  ---  ---
  Disk0     Online          223 GB      0 B
  Disk1     Online          931 GB      0 B
  Disk2     Online          238 GB      0 B

DISKPART> select disk 0

Disk 0 is now the selected disk.

DISKPART> list partition

  Partition ###  Type              Size     Offset
  -------------  ----------------  -------  -------
  Partition 1    Primary            200 MB    512 B
  Partition 2    Primary            108 GB   200 MB
  Partition 3    Primary             81 GB   109 GB
  Partition 4    Primary            128 MB   190 GB

DISKPART> list volume

  Volume ###  Ltr  Label        Fs     Type        Size     Status     Info
  ----------  ---  -----------  -----  ----------  -------  ---------  --------
  Volume 0     E   BOOTCAMP     FAT32  Partition     81 GB  Healthy
  Volume 1     C   BOOTCAMP     NTFS   Partition    562 GB  Healthy
  Volume 2     F                NTFS   Partition    529 MB  Healthy    Hidden
  Volume 3     D   WinInstall   exFAT  Partition    238 GB  Healthy

Edit: "list disk" output from existing Win10 Bootcamp installation on Internal HDD

DISKPART>
  Disk ###  Status         Size     Free     Dyn  Gpt
  --------  -------------  -------  -------  ---  ---
  Disk 0    Online          223 GB      0 B
  Disk 1    Online          931 GB      0 B

I appreciate any advice.

5
  • While “bless” command under macOS can make an external HDD the default to boot, the bless commands given in your question do not do this. The bless commands given in your question create the files named .disk_label and .disk_label_2x. To change the default to boot, the bless command would at least need to include the --setBoot option. Also, I should mention the sudo systemsetup -setstartupdisk path command has replaced the bless command for the purpose of setting the startup disk. – David Anderson Apr 17 at 22:42
  • Since I am failing to install Win10 on SSD (via Bootcamp Assistent + USB-stick) I decided to buy for a test purpose an external HDD as suggested in your guide but I did not manage to even boot into Win setup whereas in case of SSD I did but I am not able to assign/mount the EFI partition which seems to be crucial step. Currently it appears to be mission impossible. – user3602441 Apr 18 at 2:01
  • Did you use the Boot Camp Assistant to install Windows to the internal drive? If so, can you open an Administrator: Command Prompt window and post the output from the command echo list disk | diskpart? – David Anderson Apr 18 at 3:37
  • Yes in the past it was Windows 7 and then I upgraded to Windows 10 from within the OS. I've updated the question with the command output. – user3602441 Apr 18 at 14:48
  • I made the mistake of assuming your Mac had Thunderbolt 2, because the drive had Thunderbolt 2. So, I thought the Mac was a 2004 or 2005 model. These models EFI boot Windows 10. You model Mac has the original Thunderbolt. – David Anderson Apr 19 at 1:19
0

You posted in a comment: "Currently it appears to be mission impossible." Well, here is an example question, where an user had Windows installed to BIOS boot from an external drive on a 2012 Mac.

I believe your model Mac is suppose to BIOS boot Windows 10. You have a BIOS booting Windows 10 installed on the internal drive. You should probably install Windows 10 to BIOS boot from an external drive. The instructions given in your link are for installing an EFI booting Windows on an external drive.

BIOS booting Windows installations can only access the first 2.2 TB of the installation drive, when the sector size is 512 bytes. The may be a problem since your external HDD is 5 TB in size.

The Boot Camp Assistant should be able to create a USB flash drive Windows 10 installer. This installer should be bootable on your Mac. You could use this installer to try and install Windows 10 on the external drives. These drives will need to be either MBR partitioned or hybrid partitioned like the internal drive.

While the Boot Camp Assistant can create a USB flash drive Windows 10 installer, the Boot Camp Assistant probably can not be used to install Windows 10 on an external drive. This usually requires manual installation using the Windows CLI.

UPDATE

User Cordvision posted the question Big Sur: Booting Win10 from SSD and Disable Internal Drive. This question documents how a firmware update included with macOS has resulted in problems BIOS booting Windows from external drives. I found that on my 2013 iMac the Mac Startup Manager will not always display an icon or the correct icon for an external BIOS bootable drive. Also, when choosing to BIOS boot from an external drive, the Mac may instead try to BIOS boot from a different drive. To overcome this limitation, I installed the rEFInd Boot Manager. This is a free product.

Installing BIOS Booting Windows 10 on USB HDD Using 2013 iMac

These instructions will probably only work with 2012 though 2014 Macs.

I do not have the same hardware as you have. This is as close as I can get. I am also using a wireless apple keyboard and mouse. I would recommend using a wired Apple keyboard and mouse during the installation. If you have any questions about what a step does, you probably should first ask for an better explanation.

I have Catalina, High Sierra and a BIOS booting Windows 10 installed on the internal HDD. Windows 10 is installed in the partition with the identifier disk0s3. The external USB drive does not have any operating systems installed. I will be installing a BIOS booting Window 10 the partition with the identifier disk2s3. Currently, this partition contains an ExFAT formatted volume.

/dev/disk0 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *1.0 TB     disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:                 Apple_APFS Container disk1         898.0 GB   disk0s2
   3:       Microsoft Basic Data BOOTCAMP                91.5 GB    disk0s3
   4:       Microsoft Basic Data MyExFAT                 10.5 GB    disk0s4

/dev/disk1 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +898.0 GB   disk1
                                 Physical Store disk0s2
   1:                APFS Volume Muskie                  28.1 GB    disk1s1
   2:                APFS Volume Preboot                 118.9 MB   disk1s2
   3:                APFS Volume Recovery                1.0 GB     disk1s3
   4:                APFS Volume VM                      8.6 GB     disk1s4
   5:                APFS Volume Snapper2 - Data         21.6 GB    disk1s7
   6:                APFS Volume Snapper2                11.3 GB    disk1s8
   7:                APFS Volume Ron2Pasport             440.1 GB   disk1s9
   8:                APFS Volume FromTuna                35.3 GB    disk1s11
   9:                APFS Volume DavidAnderson           71.8 GB    disk1s12

/dev/disk2 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *400.1 GB   disk2
   1:                        EFI EFI                     209.7 MB   disk2s1
   2:                 Apple_APFS Container disk3         340.0 GB   disk2s2
   3:       Microsoft Basic Data BootCamp                59.9 GB    disk2s3

/dev/disk3 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +340.0 GB   disk3
                                 Physical Store disk2s2
   1:                APFS Volume RonsStuff               19.0 GB    disk3s1
   2:                APFS Volume SnapperBackup-Summer19  186.5 GB   disk3s2

If you choose to install a BIOS booting Windows on the 5 TB USB drive, then you will need to create an ExFAT formatted volume some where within the first 2.2 TB of the drive. Assuming disk5 is the identifier for your 5 TB drive, you could enter the command below to create a 500 GB partition for Windows.

diskutil partitiondisk disk5 gpt exfat BootCamp 500G jhfs+ seagate R

The steps I used to install Windows 10 to an external HDD are given below.

  1. Download and install gdisk from the SourceForge website GPT fdisk. This is a free product. First, download to your Downloads folder. Next, enter the command below in a Terminal application window to remove the quarantine.

    xattr -c ~/Downloads/gdisk*.pkg 
    

    Finally, use the Finder application to open the downloaded file and install gdisk.

  2. Use the gdisk command to insure the USB drive is hybrid partitioned. Below is what I entered in a Terminal application window. Note: According to Wikipedia, APFS partitions do not have a defined MBR hex code, so I choose to use the hex code da.

    sudo gdisk /dev/disk2
    r
    h
    2 3 
    y
    da
    n
    07
    y
    n
    w
    y
    

    Below is the output, when I entered the above.

    davidanderson@Snapper ~ % sudo gdisk /dev/disk2
    GPT fdisk (gdisk) version 1.0.7
    
    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 hybrid MBR; using GPT.
    
    Command (? for help): r
    
    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: 2 3
    Place EFI GPT (0xEE) partition first in MBR (good for GRUB)? (Y/N): y
    
    Creating entry for GPT partition #2 (MBR partition #2)
    Enter an MBR hex code (default AF): da
    Set the bootable flag? (Y/N): n
    
    Creating entry for GPT partition #3 (MBR partition #3)
    Enter an MBR hex code (default 07): 07
    Set the bootable flag? (Y/N): y
    
    Unused partition space(s) found. Use one to protect more partitions? (Y/N): n
    
    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/disk2.
    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.
    

    If you used your 5 TB USB drive with the partitioning I described above, then you would not be able to include the jhfs+ formatted partition, because this partition exists beyond the 2.2 TB limit. In this case, you would enter the commands given below.

    sudo gdisk /dev/disk5
    r
    h
    2
    y
    07
    y
    n
    w
    y
    
  3. Use the Boot Camp Assistant application to create a Windows 10 installer flash drive. Below is an image of my selection from Boot Camp Assistant included with Catalina. Do not use the Boot Camp Assistant to install Windows 10. Only create the flash drive installer from the download Windows 10 ISO file. This file can be download from this Windows website. The file I downloaded was named Win10_20H2_English_x64.iso.

    When finished, check to see if the root folder on the flash drive contains the file named AutoUnattend.xml. If found, change the name to NoAutoUnattend.xml.

  4. Download and install the rEFInd Boot Manager from the SourceForge rEFInd website. Here I will assume the downloaded zip file was expanded to the folder refind-bin-0.13.2. If you have a different folder, then make the appropriate substitutions. Note: The diskutil commands may state the volume is already unmounted and the refund-install script will produce an error message with respect to either the sed or bless command.

    Note: disk0s1 is the EFI partition on my Mac's internal drive. If this is not true in your case, then make the appropriate substitutions. In addition, you can use the EFI partition on the drive where you are installing Windows 10, as an alternative location for rEFInd.

    cd ~/Downloads
    xattr -rc refind-bin-0.13.2
    cd refind-bin-0.13.2
    diskutil unmount /dev/disk0s1
    ./refind-install --usedefault /dev/disk0s1
    echo "scanfor biosexternal" >> /Volumes/EFI/EFI/BOOT/refind.conf 
    diskutil unmount /dev/disk0s1
    
  5. Shutdown the Mac. Remove all external drive except the Windows 10 installer flash drive. Start the Mac and immediately hold down the option key until the Mac Startup Manager icons appear. Highlight the external drive icon labeled EFI Boot, then select the arrow under this icon. This will boot to Mac from the Windows 10 installer flash drive. Below is a image similar to the external drive icon you will see.

  6. The first window to appear should be similar to the one shown below. At this point, you can plug in the drive where Windows will be installed.

    Proceed as one would for a GUI installation of Windows. When a window similar to the one shown below appears, press the shift+F10 key combination.

    Note: If you press the shift+F10 key combination before the image below appears, then the Windows installer may not have loaded drivers from the Windows Support Software.

    The result should be the appearance of the Command Prompt window shown below.

  7. Enter the command given below to determine the drive letters.

    echo list vol | diskpart
    

    In this example, drives d: and f: were determined to be the ExFAT volume on the Windows installer flash drive and the ExFAT volume where Windows will be installed, respectively. If your drive letters are different, then make the appropriate substitutions in the remaining steps.

  8. If necessary, enter the command below to get the names of the available Windows installations.

    dism /get-imageinfo /imagefile:d:\sources\install.wim
    

    In this example, the name Windows 10 Pro will be used. If you choose a different name, then make the appropriate substitution in the following step.

  9. Enter the following commands to begin installing a BIOS booting Windows 10.

    Note: the first dism command will take a long time to complete. You should ignore any error messages from the second dism command.

    format f: /q /v:BootCamp /fs:ntfs
    dism /apply-image /imagefile:d:\sources\install.wim /name:"Windows 10 Pro" /applydir:f:\ /checkintegrity
    dism /image:f:\ /add-driver /driver:d:\$WinPEDriver$ /recurse /forceunsigned
    bcdboot f:\windows /l en-us /s f: /f bios
    bootsect /nt60 f: /mbr
    exit
    

    When finished , close the Windows Setup window by clicking on the red box with the X mark. In the next window, select Repair your computer, then Turn off your PC. After the Mac turns off, remove the flash drive.

  10. Start the Mac and immediately hold down the option key until the Mac Startup Manager icons appear. Highlight the internal drive icon labeled EFI Boot. Below is a image similar to the internal drive icon you will see.

    However, if you installed rEFInd to an external drive, then you should instead highlight the external drive icon labeled EFI Boot. Below is a image similar to the external drive icon you will see.

    Next, hold down the control to change the straight arrow to a circular arrow. Select this circular arrow to boot the Mac to the rEFInd Boot Manager. With the icon shown below highlighted on the rEFInd display, press the return key. If the icon does not appear, then press the esc key to refresh.

  11. Finish installing Windows 10. The computer will automatically reboot to rEFInd, then Windows 10 on the external drive. When finished installing Windows 10, plug in the Windows 10 installer flash drive and execute the Setup application in the BootCamp folder on the flash drive. Afterwards, eject and remove the Windows 10 installer flash drive before restarting the Mac.

  12. There should be an Apple Software Update application installed on your Mac. Execute this application to get updates from Apple. I would recommend installing any updates to Apple Software Update first.

  13. Finally, check with Windows Update for any additional (optional) driver and other software updates.

Additional References

Man page of gdisk
Man page of refind-install
DISM Image Management Command-Line Options
DISM Driver Servicing (.inf) Command-Line Options
BCDBoot Command-Line Options
Bootsect Command-Line Options
BIOS/MBR-based hard drive partitions
The rEFInd Boot Manager
The rEFInd Boot Manager: Configuring the Boot Manager
The rEFInd Boot Manager: Using rEFInd

2
  • That is what I tried - to use Bootcamp Assistant which successfully partitioned external SSD even if the wizard appeared it is referring to internal HDD (the screen later showed sizes of SSD so I was somehow sure I am partitioning SSD and not HDD) and prepared USB flash but during installation when I select the partition it complained that "The selected disk has an MBR partition table. On EFI systems, Windows can only be installed to GPT disks." Which seems that Win10 setup does not like Mac's hybrid compromise. If I create regular container partition I suppose Win10 won't like it neither... – user3602441 Apr 20 at 16:17
  • user3602441: I installed a BIOS booting Windows 10 to a USB drive connected to my 2013 iMac. I updated my answer with the steps. – David Anderson Apr 21 at 6:04

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