Tech Tip: How to Use Boot Camp on an External Drive

Boot Camp IconBoot Camp and Boot Camp Assistant allow you to install Windows on your Mac. It’s a nice capability that lets you select – at boot time – which operating system you wish to use: macOS or Windows.

One of the downsides to Boot Camp and the Windows installer is that it restricts you to installing Windows on your Mac’s internal drive. While Boot Camp Assistant can partition your startup drive for you to make room for Windows, there are bound to be many of you who just don’t have room to spare on your startup drive to install Windows.

Installing Windows on an external drive would be a great solution to the problem of available space, but as we said, Boot Camp and Windows impose a restriction on installing to an external drive – or do they?

There are actually a few ways you can successfully install Windows on an external drive. They range from creating clones of an existing PC installation or using Microsoft IT tools for installing Windows. But the method we’re going to outline here is a bit different. It allows you to install Windows on an external drive without first having Windows installed on a PC or in a virtual environment.

This is an advanced process with quite a few pitfalls that can trip you up. Be sure to read through the process before undertaking it. Also, make sure you have a current backup before beginning.

What You Need

  • 4 GB or larger USB flash drive.
  • Bootable external drive. We’re using a USB 3.0 drive, but a Thunderbolt drive should work as well.
  • Boot Camp Windows Support Software.
  • VirtualBox virtualization app (available for free).
  • A licensed copy of Windows 10 ISO or an install DVD.
  • Wired keyboard and mouse. During the Windows installation, the drivers for Apple wireless keyboards and mice aren’t installed until the very end of the process. If you’re not using a portable Mac with a built-in keyboard and trackpad, you’ll need a wired keyboard and mouse to complete the installation.

Prepare the External Drive for Installing Windows
The external drive that you’ll install Windows on needs to be prepared by erasing and formatting the drive for use with Windows.

Warning: The erase, format, and partitioning process will delete all data currently contained on the external drive.

1) Ensure the external drive is connected to your Mac.
2) Launch Disk Utility, located at /Applications/Utilities.
3) In the Disk Utility sidebar, select the external drive that will be used for Windows. The device will likely have the name of the external enclosure’s manufacturer listed. Do not select the volume located just underneath the device name.
4) Click the Erase button in the Disk Utility toolbar.
5) Use the dropdown menu to set the Scheme to “Master Boot Record.”
6) Use the dropdown menu to set the Format to “MS-DOS (FAT).”
7) You can use any name you wish (up to 8 characters), but we suggest naming the external WIN10.
8) Click the Erase button.

The external drive will be formatted and a single MS-DOS (FAT) volume will be created.

Prepare the USB Flash Drive for the Windows Support Software
The USB flash drive needs to be formatted to accept the Windows software that Boot Camp Assistant will download and install.

Screenshot of flash drive formatting window
(The flash drive needs to be formatted for use on Windows.)

Warning: The process of preparing the USB flash drive will delete any data contained on the flash drive.

1) Make sure the USB flash drive is connected to your Mac.
2) Launch Disk Utility, located at /Applications/Utilities.
3) In the Disk Utility sidebar, select the USB flash drive device. The device will likely have the name of the USB flash drive manufacturer listed. Do not select the volume located just underneath the device name.
4) Click the Erase button in the Disk Utility toolbar.
5) Use the dropdown menu to set the Scheme to “Master Boot Record.”
6) Use the dropdown menu to set the Format to “MS-DOS (FAT).”
7) You can leave the Name field as is.
8) Click the Erase button.

The USB flash drive will be formatted and a single MS-DOS (FAT) volume will be created.

Download Boot Camp Windows Drivers
We only need Boot Camp Assistant for its ability to download all of the Windows drivers we’ll need to ensure the install of Windows will run correctly on Mac hardware. We won’t be using Boot Camp Assistant to partition a drive or step us through the install process.

Screenshot of boot camp assistant
(The latest version of the Apple drivers that Boot Camp needs can be downloaded using Boot Camp Assistant.)

1) Launch Boot Camp Assistant, located at /Applications/Utilities.
2) In the Boot Camp Assistant window that opens, click the Continue button.
3) In the Select Tasks window, remove checkmarks from “Create a Windows 7 or later version install disk” and “Install Windows 7 or later version.” Make sure the checkbox labeled “Download the latest Windows support software from Apple” is checked, and then click Continue.
4) Select the device you wish to have the Windows support files installed on; this should be the USB flash drive you prepared earlier. After making your selection, click Continue.
5) Boot Camp Assistant will download and install the needed Windows support software on the selected device.
6) Once the install is nearly complete, you’ll be asked to provide your administrator password so the Boot Camp Assistant can change the file permissions on the USB flash drive. Provide your administrator password, and click Continue.

The Windows support software has been installed on the USB flash drive.

Use VirtualBox to Install Windows on the External Drive
This is the tricky part of the process, at least in the sense that we’re going to trick Boot Camp and the Windows installer into thinking your external drive is actually your main internal drive, or in the parlance of Windows, your C: drive.

You could perform this tricky bit of virtualization using Parallels or VMware Fusion, but we’re going to use VirtualBox because it’s free. You can download the app from the VirtualBox website.

Once you download and install VirtualBox, we’re ready to begin the installation process.

Most of the virtualization trickery will be performed from within Terminal, so go ahead and launch Terminal, located at /Applications/Utilities.

Screenshot of diskutl command
(You can find the external drive by looking for the name, type, or if this is your only external, by the location [external, physical]).
1) With the external drive that you formatted for installing Windows on connected to your Mac, enter the following Terminal command without the quotation marks: “diskutil list” and then press enter or return.
2) A list of all attached disks will be displayed in Terminal. Scroll through the list and locate the external drive you plan on using to install Windows. If you followed our suggestion earlier, it will be named WIN10, and will be of the type DOS_FAT_32.
3) Once you locate the external drive, make a note of its Identifier. The Identifier appears in the last column and will have the format of the word “disk” followed by a number. In our case, the identifier is disk4.
4) Now that we know the disk identifier, we need to eject the disk so it’s no longer connected logically to the Mac (it will still be connected physically).
5) Locate the WIN10 disk on your Desktop or in the Finder window sidebar.
6) Right-click on the WIN10 disk and select Eject from the popup menu.

Use VirtualBox to Map the External Drive to a VirtualBox Disk
The next step in the process is to map the external drive to a VirtualBox disk.

1) In Terminal, enter the following without the quotation marks: “sudo VBoxManage internalcommands createrawvmdk -filename “bootcamp.vmdk” -rawdisk /dev/disk4″ Note: Be sure to replace /dev/disk4 with the actual disk number you found from the disk identifier, and then press enter or return.
2) At the Terminal prompt, enter your administrator password, and then press enter or return.

The bootcamp.vmdk virtual disk will be created in your home folder.

Create a VirtualBox Virtual Machine for Windows
We will use VirtualBox to install Windows 10 to our external drive. We can do this because in the previous step, we mapped the external drive to a VirtualBox virtualized disk.

Virtual Box VM
(The Windows VM you create uses a virtualized connection to your external drive.)

In order for VirtualBox to be able to access the external drive, we need to launch VirtualBox with elevated permissions. Once again, we turn to Terminal.

1) Enter the following at the Terminal prompt without the quotation marks: “sudo /Applications/VirtualBox.app/Contents/MacOS/VirtualBox” Press enter or return.
2) If asked, supply your administrator password, and then press enter or return.
3) VirtualBox will open.
4) In the VirtualBox window, click on the New button in the toolbar.
5) In the sheet that drops down, enter a Name for the installation; we suggest WIN10.
6) Set the Type to Microsoft Windows.
7) Set the Version to Windows 10 (64-bit).
8) Click the Continue button.
9) Accept the default memory size, and click Continue.
10) In the Hard Disk sheet, select Use an existing virtual hard disk file.
11) Just below the option to use an existing virtual hard disk file is a dropdown menu for selecting a file to use. You may notice the menu is empty or does not contain the virtual disk file we created earlier. Click the folder icon just to the right of the dropdown menu. This will allow you to browse to the bootcamp.vmdk file, which is located in your home folder. Select the bootcamp.vmdk file, click the Open button and then click the Create button.
12) VirtualBox has created a virtual environment for us to install Windows 10 in that will actually perform the install on the external drive. The next step is to mount the Windows 10 ISO you downloaded earlier from Microsoft.
13) In VirtualBox, select the Windows 10 virtual machine, and then locate the Optical Drive. This is usually located in the Storage section of the virtual machine. Click the Optical Drive item and select Choose Disk Image.
14) Browse to where you downloaded the Windows 10 ISO.
15) Select the Windows 10 ISO, then click open.

Install Windows on Your External Drive Via VirtualBox
1) Start the installation process by clicking the Start button in the VirtualBox toolbox.
2) The Windows 10 installation will start. Follow the onscreen instructions until you come to the Windows Setup screen with the heading “Which type of installation do you want?”
3) Select the “Custom: Install Windows only (advanced)” option.
4) The Windows setup will display the currently available drives and partitions that Windows can be installed on. Because the external hard drive has been assigned to the VirtualBox machine, it is the only drive that will be listed.
5) When we used Disk Utility to format the drive, we chose MS-DOS (FAT), which is incompatible with Windows 10. We did this because Disk Utility can’t format with NTSF, but the Windows installer would recognize MS-DOS. All we need to do now is change the drive’s format to NTSF.
6) Select the drive, and then click the Format button.
7) Wait until the format is complete (the Next button will become available), and then click Next.
8) The Windows installation will start, with files being copied to the external drive.

Warning: Extremely important step follows.

9) When you see the message “Windows needs to restart” immediately shut down the virtual machine by clicking on the red close button on the window. Select “Power off the machine” from the list of options, and then click OK to power off the virtual machine.

Windows 10 Install
(Windows Setup will install the needed files to your external drive. Be sure to prevent Windows Setup from automatically restarting.)

At this point, the Windows installer has copied all the files to the external drive, and has set up a boot environment that you can start your Mac from. Next time you boot from the external drive, Windows will complete the installation process.

Restart Your Mac With the External Windows Drive
1) Close any apps you may have open, then restart your Mac.
2) Hold down the Option key during the restart. This will cause the Mac’s Startup Manager to display a list of drives you can start from. Use the arrow keys on your keyboard to select the Windows drive.
3) Your Mac will boot from the external Windows drive. The bootup process can take a while, so be patient.
4) Windows will finish the install process. At some point during the installation, Windows will restart your Mac. When it does, your Mac will restart with the normal Mac OS. You need to be present to hold down the Option key and select Windows to start from.
5) Windows will finish the installation and present you with the Windows desktop.

Getting Apple Hardware Working Under Windows
The USB flash drive you used earlier to make the Windows Support software contains all the drivers you need to install in Windows for the Apple hardware to work.

Boot Camp Setup screen
(To complete the Windows installation, run the Boot Camp Setup app to install the needed Apple drivers.)

1) Make sure the USB flash drive is connected to your Mac.
2) Click on the Windows Start button and select File Explorer.
3) In the File Explorer sidebar, select the USB flash drive, it will probably have a D or E drive letter assigned to it.
4) Open the Boot Camp folder
5) Run the Setup app inside the Boot Camp folder.
6) Follow the onscreen instructions to install the Boot Camp drivers.

Once the installation completes, all your Apple hardware, including wireless keyboards and mice, should be working.

Be Sociable, Share This Post!
Tom Nelson
the authorTom Nelson

Leave a Reply to Johannes Cancel reply

Comment

Name

375 Comments

  • Had to enable EFI in virtualbox’s settings in order to get windows to install to the drive since the disk was formatted as GPT and not MBR
    Other than that, great guide, works!

  • If I download bootcamp on an SSD but I switch computers, will I still be able to access the Windows OS? I am using a 2015 macbook pro, but I’m looking to get a new macbook soon. I need windows now, but I’m wondering if I do this whole process on my 2015 mac, will I have to do it all again on my new one? Or will everything transfer over okay because it is all saved on the SSD?

  • When creating the createrawvmdk command, it shouldn’t have quotes around the filename, in the tutorial it’s:

    sudo VBoxManage internalcommands createrawvmdk -filename “bootcamp.vmdk” -rawdisk /dev/disk4

    but should be:

    sudo VBoxManage internalcommands createrawvmdk -filename bootcamp.vmdk -rawdisk /dev/disk4

  • I tried following all the steps, PLUS allowing the VM to use EFI.
    Whenever I try to boot from the External Hard Drive, it freezes on the screen with all the boot options.

    Does anyone has any idea what went wrong?

  • Have followed these instructions a number of times now.
    Every time I start the VM it gets as far as loading files, displays the Starting Windows logo screen and gets stuck there. No additional progress, no additional information.
    The first time (and only the first time) I tried this, it copied everything on to the USB drive and got as far as the first reboot, and I cancelled the VM reboot, and restarted holding option key as advised. Since I hadn’t at that point enabled EFI, and the disc was formatted with Master Boot Record set, it didn’t appear to boot from it. I’ve even tried retracing these steps, but it still gets stuck at the Starting Windows screen now. Every time.
    I’m reformatting the USB HD and deleting the .vmdk file and removing the VM from the list in VirtualBox in between each attempt so as to start afresh with a clean config.
    I’ve used MS-DOS FAT format, GUID partition map when formatting the drive, and enabled EFI in Settings, and Use Host I/O Cache in Storage in setting up the VM.
    Anyone any ideas what’s going wrong?

    • I think it has to be formatted as NTFS. I know DOS FAT is universal, but I remember having to format the external disk as NTFS at one point. Not from the Mac OS side but using either Paragon Software or my son’s desktop PC. I think I used Paragon on my MAC. It’s been a while since I’ve done this but maybe you can find comments about that around the comments below from the last time I did this. It was about a year ago I believe. I got the info from some others between then and when this blog was first posted. I printed out the instructions and read through every single comment ever posted, notating or changing instructions where they applied. Got it to work on second try so the early comments here really helped me.

      • Thanks for your reply.
        Yes, the first (and only) time that it progressed past the Windows startup screen, Setup took me through the bit about formatting it as NTFS, and this did happen – but only that one time.
        Ever since, it just stalls on the Windows Startup screen.

      • Thanks for your reply.
        I meant to make clear that when I said “copied everything on to the USB drive”, I meant the HD, not the flash drive,
        Sorry about that.

    • Found my comment from last year. I’ll repost it here:

      “ 1) The MS-DOS formatting is for the external drive for the Windows OS, not the USB for Bootcamp support files. I formatted the external drive I was installing Win10 on as GUID / MS-DOS initially, just to rid it of all contaminants (preinstalled software and formatting.) Then … I installed the Samsung driver 1.6.0 to the Mac OS manually. Then … I reformatted the external SSD a second time, GUID / MS-DOS. The second time the EFI was successfully created. But not the first. That’s why I think it’s a driver issue. It remains MS-DOS only until the start of the Windows install. There it sees the EFI, and you select the MS-DOS partition for the OS and Windows automatically reformats it as an NTFS. So MS-DOS isn’t ever really used by Windows. If the drive were NTFS to start out, Mac OS could not work with it to integrate through Vbox etc. Thus, the shell game”

  • Followed instructions to the letter on a iMac mid 2011 and after the first restart (when you power down the virtual machine) the boot screen would only show the Macintosh HD – no sign of the external USB. On booting to mac os the external drive mounted but is wasn’t called WIN10 but had been renamed to Untitled1. Some Windows install files were there but it won’t boot from the drive. Help!

  • It didn’t work for me; my macmini ’18 booted from the external ssd drive (via USB), but I was never able to login into win 10 due to errors saying to re-install windows again.
    I then created a Win10 VM with VMWARE Fusion (latest 11.5.x version), but the external SSD drive wasn’t working as expected (it was not detected).
    Then I created a Win10 VM with Parallels Desktop (v15.1.3-47255), this time the USB SSD drive was detected; I used WinToUSB to install Windows 10 (I mounted the iso as a virtual drive) – without license it allows to install the home editions only, and apparently older windows versions (I installed the 1803).
    So if you have a MacMini ’18 and/or you’re struggling, try this way – I spent 3 days trying to find a solution… :)

  • The example actually shows disk4, not disk3. And the filesystem is NTFS, not NTSF. That said, hey, this is a brilliant tutorial. Thank you so much for writing this! I despite artificial limitations that prevent things which are technically possible so I love workarounds like this!

  • Hello.
    Brilliant!
    But what can I do if I want one more partition on this flash drive?
    I did MBR + fat32 partition + one more partition and bootcamp can’t download drivers to it.
    Could I just format it to single partition, then download bootcamp drivers, move them to safe place, partition my drive and put drivers back?

  • I have run into a problem where I cant install Things that require a restart (like bootcamp drivers). I just get a folder icon With ? on it. Do you know how to fix that?

  • I’ve followed the directions on my mac min. When I get to the part where we reboot to windows I receive the message,”Preparing Automatic Repair” and it’s like my computer is stuck in a loop restarting over and over again by itself and coming to the windows screen the little circle bubbles and then this message.

    • I re-followed all the steps and realized I missed powering off the virtual machine. Thanks for the great instructions.

  • I am not able to format in the drive selection start up process. System does not allow me to format the SSD as the format click button is not enable.In the process it has mention to format and proceed as the format click is not enable ,I am not able to proceed. please help or any thoughts on this

  • This guide is a little outdated, at least for newer macs:
    1/During the DiskUtility USB Flash Drive preparation, use GUID partition map, not MBR – Without that your Mac will not allow booting from it.

    2/When you create your VM on virtualBox, enable EFI in Settings->System – This will allow the VM to properly recognize the drive and windows to install using EFI.

    • Been going in circles with this. I tried as described in article. No luck. Saw comment about EFI so I tried that. It gave me an error in VBox on start. Tried the steps again, this time it worked and I got to the install process but WINSTALLER said can not install on EFI drive so I erased inside installer and got a new drive with the EFI allocations. Going well.
      UNTIL it got to “installing updates” section and hung…. no movement for HOURS so tried closing VBox and got error on restarting the box. Crapped out… have to start over.
      When trying again, I keep getting the VBox error if enable EFI. Multiple attempts. Now trying again without EFI enabled. Will erase and create a NEW drive in installer and see if that helps.

      Anyone smarter than me care to write an app so we can all simply just tell windows to install from the ISO on boot?

      • Did you do:
        When you create your VM on virtualBox, enable EFI in Settings->System – This will allow the VM to properly recognize the drive and windows to install using EFI.

  • Trying this and get to the “Use VirtualBox to Map the External Drive to a VirtualBox Disk” step. I enter in the commands exactly as listed for disk3 (in my case)

    sudo VBoxManage internalcommands createrawvmdk -filename bootcamp.vmdk -rawdisk /dev/disk3

    enter in my admin pw, but then i get an error:
    VBoxManage: error: Cannot open the raw disk ‘/dev/disk3’: VERR_FILE_NOT_FOUND
    VBoxManage: error: The raw disk vmdk file was not created

    anyone know how to resolve

    • Yes, you need to change VIEW menu in Disk Utility to ALL DEVICES, then you can actually erase the usb drive with masterboot option.

    • OK. That didn’t do the trick. You need to unmount the disk, not eject it. Just connect the flash drive and then type:
      diskutil unmount /dev/disk2s1
      replace the disk2s1 with whatever you have there it would be disk3s1 in the article. And voila :D

  • For some reason this doesn’t work on a Mac Pro 2019 running in my case, the W5700X and dual XDR displays.

    I’m able to use this process successfully on a MacBook Pro from 2016, and boot and run windows off an external thunderbolt drive no problem. The same installation, just crashes immediately after the windows logo on the Mac Pro 7,1.

    Not sure what’s up with that. Of course, the T2 security is set to off. No go.

    Any ideas?

  • i’m following your steps by steps and i’m not able to find thebootcamp.vmdk file in VirtualBox manger, i’m using mac OS Catalina. I would like to install windows 10 on my external hard drive to save room on my mac, i’m stuck at this point could you help me thanks

  • For my MacBook Pro 15″ 2017 (MacBookPro14,3) I had to change some steps to get Win10 running. Here are my steps, in short:

    Before you begin, install VirtualBox and download device drivers onto a FAT-formatted USB stick using Boot Camp Assistant. Keep a USB mouse handy (& keyboard if you don’t like the on-screen one). Neither touchpad nor keyboard worked for me during win setup!

    1) In Disk Utility.app: Format target disk drive as FAT (MS-DOS) with GUID Partition Map

    2) Unmount target drive (eject it, but don’t unplug it)

    3) In Terminal, run:

    sudo VBoxManage internalcommands createrawvmdk -filename bootcamp.vmdk -rawdisk /dev/disk2

    (disk2 in my case, check “Device:” in Disk Utility)

    4) Unmount target drive again (eject it, but don’t unplug it)

    5) In Terminal, open VirtualBox as root:

    sudo /Applications/VirtualBox.app/Contents/MacOS/VirtualBox

    6) Create new VM:
    – Name: Win10 (VirtualBox guesses the os from that)
    – Use an existing virtual hard disk file (bootcamp.vmdk)
    – Create

    7) Click Settings->System and tick the box “Enable EFI (special OSes only)”, close settings.

    8) Click SATA Port 1: Add your win10 ISO

    9) Start VM and press a key immediately when asked (otherwise it quickly boots into a grub shell)

    10) In the setup, format the big partition (the one not named EFI) and start the install. PREPARE FOR NEXT STEP!

    11) When it wants to reboot, power the VM off immediately. You have 10 seconds.

    12) Restart Mac holding option (alt)

    13) Boot from “EFI Boot” and complete the installation. Hold option when it auto-reboots during install, or you’ll have to wait for macOS to boot and then restart into Win again…

    • Hello, your comment was very helpful to me, but when im using the windows 10, it restarts all the time because “one error has occurred”; maybe you can help me with that.

      Also, I’ve tried to boot windows 7, but the shell in the VM always open, and if I touch the esc key, goes to a menu where I believe im supposed to select the boot from dvd option, but when I do it, a black screen open and close very quickly, any ideas?

    • Thanks. This got me further so I can boot from the “EFI boot” drive and I see the blue windows installer starting up but a minute later it says an error has been found (stop code: INNACCESSIBLE_BOOT_DEVICE) and restarts.

  • My mac apparently partitioned the disk as GPT, which Windows would not install on. I kept formatting the disk inside the windows VM and it got to NTSF but is still a GPT partition. How can I fix this so that windows will install?

    • enable EFI on the VM – See my comment:
      This guide is a little outdated, at least for newer macs:
      1/During the DiskUtility USB Flash Drive preparation, use GUID partition map, not MBR – Without that your Mac will not allow booting from it.

      2/When you create your VM on virtualBox, enable EFI in Settings->System – This will allow the VM to properly recognize the drive and windows to install using EFI.

  • Thanks to this guide, many helpful comments, and specifically the additional guidance from Alessandro Morandi…

    https://medium.com/@simbul/how-to-boot-windows-from-an-external-hdd-ssd-on-a-macbook-bdcf99a721c7

    …I have succeeded in creating an external Windows 10 Bootcamp which runs natively on my MacBook Pro (mid 2012).

    However, I cannot open it using Parallels 11 from within OSX 10.11.6

    Has anyone achieved this? and if so, can you please offer some tips on setting up Parallels to recognise the external drive?

  • hi, im having a problem at step 11. when making the vmdk in terminal, it says “error: the raw disk vdmk file was not created” although i did not have any typos, and put the right command, including the correct disk number. any help?

  • Hi, I’m having trouble at step 1 of :Use VirtualBox to Map the External Drive to a VirtualBox Disk

    I have done everything as it says, and I substituted disk4 for, in my case, disk2, so the command is as follows:

    sudo VBoxManage internalcommands createrawvmdk -filename “bootcamp.vmdk” -rawdisk /dev/disk2

    But I keep having the following error:

    VBoxManage: error: Cannot open the raw disk ‘/dev/disk2’: VERR_FILE_NOT_FOUND
    VBoxManage: error: The raw disk vmdk file was not created

    Can you help me?

  • Hi, I’m having some trouble at step 11 of the process to ‘Create a VirtualBox Virtual Machine for Windows’ – I keep getting an error message that VirtualBox can’t open the ‘bootcamp.vdmk’ file in the Home folder. Any suggestions??

    • Your external disk probably connected again. Use the eject button to “eject” the drive and try again!

      • That did the trick, thanks!

        Unfortunately I’m now having issues trying to format the drive while installing Windowsill – I click format, then OK to confirm I want to format the drive, and then nothing happens!

        Don’t suppose you have any suggestions for this issue too?

  • I tried a few ways but only this worked for me:
    Needed: USB flash drive 8GB or more, Windows iso, VirtualBox + Extension Pack, WinToUSB (https://www.easyuefi.com/wintousb/) and of course the external drive. WinToUSB free works with Windows10 Home. Please read info on their site for other Windows versions.
    Use Bootcamp Assistant to download the Windows Support files (you might need to click in the menu for Action).
    Use Disk utility to format the USB flash drive to exFAT and the external drive to GUID HFS+ or FAT
    Copy the Windows iso, Windows Support files and WinToUSB to the USB flash drive and eject.
    Install VirtualBox and Extension Pack. Start VirtualBox and make a Windows10 virtual machine (VM), be sure the USB port is enabled.
    Start the Windows VM. Attach the USB flash drive and the external drive that you want Windows on.
    Copy the files from the flash drive to the VMs desktop.
    Install WinToUSB. Open WinToUSB and select the Windows iso as source and the external drive as goal. Let WinToUSB do its work. Wait until it says 100% and then (important:) click HOME. Now copy the Windows Support files to the external drive.
    Close the VM and VirtualBox and reboot. As soon as you hear the startup sound hold the Alt-key until you see the options for startup. Choose the EFI disk.
    Now you have to install Windows. When finished, open the Windows Support folder and click setup to install the Bootcamp-drivers.
    Done!

  • When you have no sound please do not reinstall. It is unnecessary. Locate the AMD sound device in devicemanager. Select update driver and select the driver folder on the Bootcamp USB stick. The driver will update.

    I tried updating all audio devices and Game audio devices and after that I did have sound.

    Also in my case there were a few devices that didn’t install. Select them too and search for drivers on the Bootcamp USB stick driver folder.

  • Hello,

    Thank you for this! I know this comment is coming kind of late but I’ve had difficulties with the booting process. Everything installs fine, but after I close VirtualBox and restart with the option-key, I only have the one option to pick from– my mac hard drive. Do you know how to fix this?

    • I found that if while I was in the startup disk selection screen and the external drive wasn’t appearing that If I unplugged and plugged back in the external drive that it would show up. Not a perfect fix or any sort of explanation as to why it doesn’t show up automatically but ¯_(ツ)_/¯

  • So I get to the step where I’ve finished the installation with the virtual machine. I go to restart my computer in windows using the external drive but like some other people it doesn’t appear. I find that if I unplug it and plug it back in then it shows up… however then when I select it and press enter it just loads to a black screen and does nothing….

    I’ve tried going to Recovery mode and utilities to select no security, ive also tried giving full access to system preferences…. neither option seemed to help.

    SOS

    • having the same problem i cannot boot the drive after installed on the virtualbox after reboot. it says it can’t find a bootable drive or something like that and just the standard dos black screen won’t go any further. the install worked great and closed it down at the restart screen now it won’t boot. any help would be appreciated. is it because you need a certain usb drive to do this? or will any usb hard drive work? running a macbook pro 2011 if that helps 2.8ghz

  • hello,

    I try the process you describe and here is what happened :

    Last login: Sun Apr 5 19:18:03 on ttys000
    tv:~ JP$ diskutil list
    /dev/disk0 (internal, physical):
    #: TYPE NAME SIZE IDENTIFIER
    0: GUID_partition_scheme *250.1 GB disk0
    1: EFI EFI 209.7 MB disk0s1
    2: Apple_HFS Mac 249.2 GB disk0s2
    3: Apple_Boot Recovery HD 650.0 MB disk0s3
    /dev/disk1 (external, physical):
    #: TYPE NAME SIZE IDENTIFIER
    0: FDisk_partition_scheme *248.0 GB disk1
    1: DOS_FAT_32 BOOTCAMP 248.0 GB disk1s1
    tv:~ JP$ sudo VBoxManage internalcommands createrawvmdk -filename bootcamp.vmdk -rawdisk /dev/disk1
    Password:
    VBoxManage: error: Cannot open the raw disk ‘/dev/disk1’: VERR_FILE_NOT_FOUND
    VBoxManage: error: The raw disk vmdk file was not created

    What can I do, Could you help please ?
    best regards
    Jean-Pierre

  • Thanks for your procedure. I’m having a challenge:MacBook-Pro-3:~ jeffjohns$ sudo VBoxManage internalcommands createrawvmdk -filename “bootcamp.vmdk” -rawdisk /dev/disk2
    Password:
    VBoxManage: error: VMDK: could not open raw disk file ‘/dev/disk2’
    VBoxManage: error: Error code VERR_RESOURCE_BUSY at /Users/vbox/tinderbox/6.0-mac-rel/src/VBox/Storage/VMDK.cpp(3426) in function int vmdkCreateRawImage(PVMDKIMAGE, const PVDISKRAW, uint64_t)
    VBoxManage: error: Cannot create the raw disk VMDK: VERR_RESOURCE_BUSY
    VBoxManage: error: The raw disk vmdk file was not created

    Do you have any suggestions?

    Thanks again!

    • I was having this problem, too. The problem was that the WIN10 drive had remounted. I unmounted it and ran there terminal command again, which then worked.

  • I tried this method but Bootcamp assistant will not open. It throws the message “External storage device attached.” I am pretty sure my formatting of the drives is correct.

    • I had the same error. Click ok, then got to action (on the top bar) > Download windows support software, and choose your USB drive as the destination

  • I had problems with MBR, GPT incompatibilities. the macOs disk utility formatted with GPT, but windows didn’t like it.

  • I’m stuck at the terminal section when entering the disk:

    Nouras-MacBook-Air:~ Noura$ sudo VBoxManage internalcommands createrawvmdk -filename “bootcamp.vmdk” -rawdisk /dev/disk12
    Password:
    VBoxManage: error: VMDK: could not open raw disk file ‘/dev/disk12’
    VBoxManage: error: Error code VERR_RESOURCE_BUSY at /Users/vbox/tinderbox/6.0-mac-rel/src/VBox/Storage/VMDK.cpp(3426) in function int vmdkCreateRawImage(PVMDKIMAGE, const PVDISKRAW, uint64_t)
    VBoxManage: error: Cannot create the raw disk VMDK: VERR_RESOURCE_BUSY
    VBoxManage: error: The raw disk vmdk file was not created

      • I have done that step to eject it (but kept it in physically) but still getting the same error:
        Nouras-MacBook-Air:~ Noura$ sudo VBoxManage internalcommands createrawvmdk -filename bootcamp.vmdk -rawdisk /dev/disk12
        Password:
        VBoxManage: error: Cannot open the raw disk ‘/dev/disk12’: VERR_FILE_NOT_FOUND
        VBoxManage: error: The raw disk vmdk file was not created
        Nouras-MacBook-Air:~ Noura$ sudo VBoxManage internalcommands createrawvmdk -filename bootcamp.vmdk -rawdisk /dev/disk13
        VBoxManage: error: VMDK: could not open raw disk file ‘/dev/disk13’
        VBoxManage: error: Error code VERR_ACCESS_DENIED at /Users/vbox/tinderbox/6.0-mac-rel/src/VBox/Storage/VMDK.cpp(3426) in function int vmdkCreateRawImage(PVMDKIMAGE, const PVDISKRAW, uint64_t)
        VBoxManage: error: Cannot create the raw disk VMDK: VERR_ACCESS_DENIED
        VBoxManage: error: The raw disk vmdk file was not created

      • So I get to the step where I’ve finished the installation with the virtual machine. I go to restart my computer in windows using the external drive but like some other people it doesn’t appear. I find that if I unplug it and plug it back in then it shows up… however then when I select it and press enter it just loads to a black screen and does nothing….

        I’ve tried going to Recovery mode and utilities to select no security, ive also tried giving full access to system preferences…. neither option seemed to help.

        SOS

        • Mate I’ve got the same problem, windows immediately tries to fixing mode as soon as I boot into the external drive. To fix this I went back and made sure efi was checked but then when I select efi in VM I cannot format the disk to NHFS.

  • I have followed the guide and the installation with the virtual machine went trough.
    Now I restarted my system and press option on the keyboard but only my Macintosh HD shows up if I go through recovery mode and select the startup disk I can see it but it says I can’t change the boot drive.
    I am on a mac pro 6,1 running Catalina.
    Any idea?