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How to Use Boot Camp on an External Drive to Run Windows on a Mac

Boot Camp Assistant Icon

Boot 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 only 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 to Install Boot Camp on an External Drive

  • 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.” Ensure 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 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 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.
  9. Warning: An extremely important step follows…
    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 on-screen instructions to install the Boot Camp drivers.

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

Tom Nelson
the authorTom Nelson
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  • Hello, after following the guide I went on and replaced the optical bay with the external ssd.. and guess what? I can’t start windows. I am guessing it has something to do with the disk identifier? Any guesses or ideas?

  • I followed everything but I keep getting No bootable device — insert boot disk and press any key on first Windows boot.
    So after the restart I pick Windows and this thing pops up. Got no idea how to solve it

  • So everything works great until I need to install the drivers, when I click on setup it gives me error, furthermore during the windows setup it doesn’t find my wi-fi net so windows is not connected to internet because it doesn’t have the drivers.

  • Everything works fine until the first restart from the external drive. I’m able to select the Windows volume but the screen remains black then, nothing happens. Also, no activity seems to go on since the R/W LED on the drive doesn’t flicker.
    Any ideas what could be the catch?
    MBPro mid 2014, Catalina, external 125GB Samsung SSD in a USB3 case.
    Thanks in advance!

  • Thanks to Tom Nelson for a great article. It worked like a champ for me running Catalina on an iMac and installing BootCamp to a 1TB Seagate drive.

    I was trying to help my son who is having a problem installing BC on his MBP running Mojave. His MBP keeps complaining that he does not have enough disk space to continue even though he’s deleted over 40G. He’s 500 miles away attending grad school and needs to run a Windows only program. Parallel Desktop and other virtual machines will not work with the license he needs to use.

    I can boot into the disk on the Catalina machine, but he is not given the option on his Mojave machine.

    Any ideas?

    • Believe it or not, the likely cause is still not having enough free space. Back in the early years of Boot Camp, very little free space was required, on the order of 20 GB, though I think the default was set at 30 GB.

      Over time, and with new versions of Boot Camp and Windows, the minimum free space requirements has gone up. Currently Apple says 50 GB in the smallest amount to use, but in an Apple technical bulletin, they say 55 GB is the minimum for Boot Camp.

      I would suggest you shoot for getting 60 GB freed up and then try installing Windows using Boot Camp Assistant.


  • Hi
    Thanks for a very well explained article, pity for a couple of things not so easy to understand:

    1) In Terminal, enter the following without the quotation marks: “sudo VBoxManage internalcommands createrawvmdk -filename “bootcamp.vmdk” -rawdisk /dev/disk4″ – If you remove the quotation will you leave the space in between or not? I tried both but it didn’t´t work.

    2)In terminal I got “Syntax error”!!!

    3) In the Disk Utility the “volume located just underneath the device name” was the only one I was able to format with MS-DOS (FAT)

    4) The file in the so called home folder was never to be found.

    OBS I prefer the Win 7 Ultimate instead of Win 10 and I have a iMac 2010 running with Sierra

    Thanks anyway

  • Windows Cannot be installed to the disk. The selected disk has MBR partition table. On EFI systems, windows can only be installed to GPT disk.

    Help I have done this three times followed all the directions and get stuck here. I have a 2017 iMac running Catalina and the hard drive is a Samsung X5 Please someone help before I jump out my first floor window

  • Can anyone tell me how to convert the MBR partition to GPT. I have a Samsung X5 external hard drive and I’m at the last few steps.

    This is why I hate PC’s Never goes easy

  • Not read all the comments yet on here but I’ve a hit a snag when I get to Install Windows and you have to format the drive to NTFS this is not possible. Tried twice now with same result.

  • I have tried to install Windows 10 on an external drive but the set up is still looking for Parallels Desktop which I tried some time ago. This was uninstalled months ago and setup.exe does not recognise VirtualBox which I have now. Is there a way of getting around this and can I rid the system of any trace of parallels desktop?
    I am running Catalina on the Mac and have an external drive formatted ready for use. Windows support software is downloaded on a correctly formatted USB.

  • Has anyone been able to install Win10 on Bootcamp on an external drive on a T2 chip machine (in my case 16″ MBP) running the latest Catalina? If so, how did you get it to work please? Thanks!


    VBoxManage: error: VMDK: could not open raw disk file ‘/dev/disk1’
    VBoxManage: error: Error code VERR_RESOURCE_BUSY at /Users/vbox/tinderbox/5.2-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

    TO FIX:

    First make sure your external HD is attached. Then find out what device node your HD is. In your case it’s /dev/disk2. Umount it with

    run command
    diskutil umountDisk disk2

    and wait until it disappeared from Finder. Change the owner of the device node to your user:

    run command:
    sudo chown whoami /dev/disk2

    Then re-run the command below and you’re done with the fix
    sudo VBoxManage internalcommands createrawvmdk -filename “bootcamp.vmdk” -rawdisk /dev/disk1

    • The disk command runs successfully once the drive is ejected, but the “bootcamp.vmdk” file is a text document of 540bytes.

  • it still does not work it gives me a error message on the last step

    error:Windows cannot be installed to this disk. The selected disk has a MBR partition table.On EFI systems, Windows can only be installed on GBT disks

  • I did it to a new MAC Pro 2019 (16″) in EFI mode – all is working except audio. The driver is “Apple audio device” – showing no error but I have no sound. Any fix for this ? (I did not tried any BIOS emulator or DSDT modification)

    thank you

  • The Oct 15 comment by “force” mirrors my experience exactly with a Samsung X5 SSD (1 TB instead of 500GB, and the recognized partitions mentioned are precisely double the size of his/hers) — the method I used was a refinement of the one on this page, described in the following video…: https://www.youtube.com/watch?v=910Y1hLreRc

    I’m using the Nov19 Windows ISO, btw…

    Need to get this up and running — any suggestions are more than welcome!

  • All good up until the restart point. Unlike many others, when I restart and hold option I do get the Windows option and can select it. However, rather than finishing the installation, I get the blue windows logo for a minute or so before the message: “Windows installation cannot proceed. To install Windows, click “OK” to restart the computer and then restart the installation.” I have obviously followed these instructions multiple times without success.

    Any ideas how I can fix this?

  • 2019 16″ MBP on Catalina 10.15.1

    I get as far as run Boot Camp Assistant, when I do, I get this error:

    External storage device Attached.

    Please remove any external storage device attached to this system before continuing.

    ?? If I continue with the external drives unplugged, then it just gives an option to install bootcamp on the internal hard drive.

  • Hi all,

    Found a fix for the EFI boot problem. Where hold option after installing windows won’t display the windows disk.

    Fix starts at the time of Windows install. Everything in the tutorial is good until getting to the Windows install through virtual box.

    Instead of clicking through the normal install process select “repair your computer” > “troubleshooting” > “command prompt.” enter the following commands, being sure to select the disk you’ll be using for the install:

    list disk
    select disk nn (where nn is the disk you will be erasing)
    convert gpt
    create partition efi size=100
    format quick fs=fat32
    create partition primary
    format quick fs=ntfs

    Power off the the virtual box
    Restart the virtual box and install normally to the new large partition you’ve created.
    Let the entire process finish and restart, don’t cancel it early per the tutorial here.
    Complete the windows setup prompts (including creating a login, password, security, etc).
    Once completed shut down the virtual box
    Restart your Mac and hold the option key to select a startup disk
    You should be able to select EFI at this time and boot into windows (note I had to restart 2-3 times before it fully logged in. Gave me a couple blue screens in the process).
    Act quickly: once booted and logged in use the bootcamp disk you created earlier to install the necessary drivers. Taking too long can create some very interesting issues with the display dimensions.

    I completed this last night and it’s been fairly stable. Not perfect, but time will tell.

    Machine: High Sierra 2017 27″ iMac 4.2 i7, 64GB Ram, 8GB 580. Installed on external Sandisk Pro SSD.

    • Tried this, but it fails to install on the primary partition

      “Windows cannot be installed to this disk. The selected disk of the GPT partition style”

      this remains the same despite reformatting it

      • I was able to get past this problem by modifying the boot settings on the virtual machine to use EFI instead of BIOS. Then hit any key at startup and it boots off of the virtual DVD drive.

    • Thank you so much, I had the same issue and I followed your guide and everything works perfectly smooth now.

      My specs : MBP 2016 with OSX 12.6 Sierra & Windows 10 (nov 2019) installed on a Samsung SSD T5

  • I see many people who cannot boot the EFI volume. I banged my head against that particular wall for a long time, but I think the answer is to turn off your MacBook’s Startup Security.

    See Apple’s documentation for instructions: https://support.apple.com/en-us/HT208198
    You need to pick “No Security” under Secure Boot and “Allow booting from external media” under External Boot.

    I’ve also put together a post with all the tricks I had to use to get the whole process to work: https://medium.com/@simbul/how-to-boot-windows-from-an-external-hdd-ssd-on-a-macbook-bdcf99a721c7

    • Thanks Alessandro! This has made all the difference to me. Your post has enabled me to successfully install windows10 on an external SSD and it’s working perfectly on my MacBook Pro 2014!

  • I’ve been trying to do this for almost 2 weeks now. Getting closer and closer with each day. But at the moment I’m stuck and I can’t seem to find any help
    So please if anyone could help me:
    I installed the Windows cool cool – then when I reboot my mac and boot from Windows:
    1. First I got an error saying that my windows has to be repaired and that I should insert an installation disk and restart – if I mount the disk in VirtualBox it only let’s me install it again there’s no repair option.
    2. I read some comments that said that I should let the virtual machine restart and finish setting up on the machine. I did that and with that when I reboot i get a blue screen of death for 1 second (can’t really read it) and it reboots over and over.

    Any help would be appriciated :)

  • Hey, I’ve followed the guide on a Samsung X5 SSD (Thunderbolt) on my 2018 MBP – everything works fine until I get to the Drive Selection page in the setup process. The EFI-Volume doesn’t appear, instead (on a 500GB Volume) Windows appears to recognize a 58GB partition and 450 GBs of free space. It won’t let me install because Windows recognizes the drive as a MBR-Partition-Table while in diskutil it is clearly listed as GUID-partition-scheme
    0: GUID_partition_scheme 500.1 GB disk1
    1: EFI EFI 314.6 MB disk1s1
    2: Microsoft Basic Data WIN 499.8 GB disk1s2
    Any ideas on that? Drive is properly formatted, been trying for 5 hours and im starting to become desperate

  • Did someone get it to work on a 2019 MacBook Air? It installs correctly and USB mouse works but not all the hardware. WLAN did work with BootCamp installed and I got some drivers but no trackpad or internal keyboard support.

  • Installation succes but after i shutdown and on the macbook and hold the option button theres no other drive. Only macintosh hd. Please help me to fix. Thank you.

  • Hello, im trying to install win10 on mac Mojave 10.14.6

    I followed the instructions and the issues in the comments until the boot device showed up

    but after running it. Mac log will show and and box telling me that i need to reinstall the mac OS.

    one thing that didnt work for me and I dont know if it will effect the process. while installing win10 on the hard disk I cound not Format the disk from inside win.

    EFI and O/I are enabled. the first erase for the Hard drive is GUID MS-DOS (FAT)

    Thank you

    • I’ve not had a successful install yet, but I encountered the same problem in previous attempt ie not being able to format the drive in Windows. I ended up formatting the target drive and USB flash drive using Tuxera Disk Manager as NTFS before starting the whole process. Alternatively, if you have access to a Windows PC you could format the drives using it.

      It worked fine after that.

      Now I can install Windows 10 Pro on the target drive but can’t get a Windows boot disk showing when using Alt/Option key on Macbook start up, as noted by other.

      There are errors Ive found (and fixed with trial and error) with the set up as written up, but it is quite dated after all.

  • I wonder if this would work with a partition in the internal drive. I have a SSD drive which is not the original Apple one (it was too small) but the new one does not support Bootcamp. I wonder if this procedure may help me install Windows 10 in a different partition of internal disk without using bootcamp

  • I managed to follow the process but in the end, when I powered off the virtual machine and restarted holding Options key, my mac was trying to install win 10, everything seemed good until bluescreen appeared…and restarted in a flash that I even couldn’t read the error message…
    Any suggestion please?

  • Can someone tell me the purpose of installing and running Windows from an external drive instead of internal drive?

    The reason I ask, I have a Macbook Pro from 2009 that is too slow/underpowered to run Windows 10 on VirtualBox. If I use an external drive for Windows instead, will Windows run quicker when connected to the Macbook?

    • You might not have a ton of space on your internal drive, or for me I have 2 computers and I only use Windows for specific software, so it makes sense to be able to carry it with me. If you have an external SSD, and your internal drive is a hard disk, I think it should be faster. But USB is not as fast as SATA, so if they’re both the same (SSD or HDD), maybe not.

  • The first virtualbox command failed with VERR_FILE_NOT_FOUND. I tried with the thumb drive still connected, and got a busy error. Solution was to use disk utility and eject just the partition (disk2s1), leaving the drive (disk2) alone.

  • Failed to open a session for the virtual machine WIN10.

    The virtual machine ‘WIN10’ has terminated unexpectedly during startup with exit code 1 (0x1).

    Result Code: NS_ERROR_FAILURE (0x80004005)
    Component: MachineWrap
    Interface: IMachine {5047460a-265d-4538-b23e-ddba5fb84976}

    Please HELP

  • So the whole process worked great for me. No issues.

    But is it possible to start up Virtual Box with this Windows computer I now have contained on a USB drive?

  • Hi all,

    I followed these steps and the one’s included on Sven’s Medium page. However, once I restart the Mac then input my Wireless info and select the ‘Boot EFI’ drive to boot into it immediately goes to the Apple logo, loads, then displays a message in Boot Recovery Assistant that ‘An Internet connection is required to verify this start up disk’. Even after reconnecting to my network it just boots into OS X.

    Has anyone else experienced or solved this issue?

    2018 Macbook Pro
    Mojave 10.14.3

    Samsung T5 SSD

    VirtualBox 6.0.10

    Windows Home 64-bit, newest ISO release


  • This worked finally. I have to try multiple times with different hits and tries. For my case, I am writing down what i did, if it helps anyone here.

    Laptop model: Macbook pro mid 2012 retina
    External hard disk used: 160 GB Toshiba (Actually taken out from my PS3 console :p)

    Failures and their alternatives followed:

    Downloading Boot Camp Windows Drivers on external usb always failed for me. For some reason, after downloading for 30 minutes and at an end, the Boot Camp Assistant gave error unable to save windows support software on selected drive.
    When starting Boot Camp Assistant, “Download Windows Support software” option is in Action menu on top and it asks for saving it anywhere on your mac drive. Downloaded it locally and then manually copied it to my USB external drive.

    When Creating bootcamp.vmdk, I was getting I/O read error showing as its already in use.
    Make sure the External Drive on whom you want to install windows is ejected and run the command in terminal again.

    After bootcamp.vmdk creation, my mac automatically mounts the external drive. which caused it not to be used in virtual box installation.
    After running command on terminal for rawdisk bootcamp.vmdk creation, again eject your drive and don’t include quotes around bootcamp.vmdk

    I was using some old Win10 ISO lying around and it was not booting on mac after all steps and installation.

    Download official win10 64bit iso from windows site. It worked for me.

    After completing all steps, installed bootcamp drivers on windows, rebooted couple of times, everything worked except I am unable to open Bootcamp control panel on windows 10 to configure touchpad click and sensitivity etc.
    It gave error “Bootcamp can’t access startup disk..”

    I was not able to find its solution so far. Maybe its because bootcamp expects the installation of windows to be on MAC drive rather then on external drive.
    Any help in solving this problem will greatly help.

  • This worked for me after trial and error with some of the updates on the procedure. I installed in a Samsung T5 1TB SSD, using a MacBook Pro 13″ 2017 version.

    after successfully making everything work I went greedy. I decided to shrink the 1TB partition within Windows, so I could re-purpose it and reuse it in MacOS. I created a G: approx. 500MB large as simple volume of exFAT. I then went into MacOS, where G was visible and I instructed disk utility to erase that and make it MacOS journaled etc. I got an error about not enough space, and after that, when I boot the MacBook I don’t get the window10 boot drive when I hold down option key. I’m suspecting perhaps disk utility deleted the EFI boot partition Windows had created? I’m lost. Now Windows 10 is locked inside the SSD and I am not sure how to access it from my Mac…

  • Failed to open a session for the virtual machine WIN10.

    VD: error VERR_NOT_SUPPORTED opening image file ‘/Users/fatehsyed/bootcamp.vmdk’ (VERR_NOT_SUPPORTED).

    VD: error VERR_ACCESS_DENIED opening image file ‘/Users/fatehsyed/bootcamp.vmdk’ (VERR_ACCESS_DENIED).

    Failed to open image ‘/Users/fatehsyed/bootcamp.vmdk’ in read-write mode (VERR_ACCESS_DENIED).

    AHCI: Failed to attach drive to Port0 (VERR_ACCESS_DENIED).

    Result Code: NS_ERROR_FAILURE (0x80004005)
    Component: ConsoleWrap
    Interface: IConsole {872da645-4a9b-1727-bee2-5585105b9eed}


    • Make sure External drive is ejected. I had same error. Mac mounted the drive automatically after running bootcamp.vmdk creation command at terminal.

    • This worked for me after getting the same error:

      Under Settings -> Storage choose the main root controller and check the “Use Host I/O Cache” as enabled.

  • When i restart my mac, the external drive is not shown as an option to boot from – how can i fix this?

  • I got to the reboot point, and the WIN10 drive won’t show up, seems like others also have this issue, but I don’t see a solution. Anyone know how to get the EFT partition in there? I don’t know the deal with that.

    • There are many, many posts below in comments for that exact issue, all the way back to the earliest comment. I even left help about it a couple or few times. Good Luck!

    • While im sure it’s too late for you, I had this issue too and it turns out I didn’t open virtualbox with elevated permissions. Be sure to follow this step posted above, as I missed it:

      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.

  • Hi, thanks for the tutorial! If I am using Parallels instead of VirtualBox how is the
    “sudo VBoxManage internalcommands createrawvmdk -filename “bootcamp.vmdk” -rawdisk /dev/disk4”
    command changed? Does it change other parts of the process? Any help is appreciated!

  • Great jobs. I followed the procedure and now windows 10 pro works perfectly in my iMac 21,5 late 2013. I’ve installed windows in a Samsung SSD t5 250 GB.
    Thank you very much.

  • This procedure does not work. I have tried it multiple times and follows the procedures exactly.

    A 2019 iMac 4k (6 core/16GB/256GB) will NOT boot off of a USB drive. I have a Samsung SSD T5.

    • I think would be helpful to know I’d this is because it’s a 2019 and that’s how Apple designed their new Macs or not, because I have successfully done this procedure twice in the past year, on a 2015 MacBook Air Mojave, and a 2012. T5 is good because it installs the smoothest to that SSD. However, I did not follow the procedure “exactly”. I don’t believe the original writer updates the instructions anymore, and early on relied on replying to comments and questions as his update.

      Here is what I do and what I suggest anyone do: I first read through all the comments below, all of them, right back to the time it was originally posted because the writer answers in many of those and added additional instructions or explanations. I printed off the original instructions and made notes on each section where comments by others mattered or changed it. Then I attempted to do it. I ran into some things as most people will with so many different models and peripheral specs, but they were easily resolved by either the comments below, or a bit of trial and error. Three days is the longest the first install took, the second one was an hour and a half.

      It does work. But I think you need to pay close attention to many comments and questions below and adjust the instructions accordingly. It is well worth that effort and extra time.

  • I have come to the last part of the tutorial, but everything goes perfect, but I can’t choose the boot drive when I’m booting the computer again??? Please help. I can’t figure it out.

    • Did you ensure that the external drive with Windows has the EFT partition too? That is what is needed to see it as a boot selection.

  • I’m running into an issue for the final step. I got everything completed, Windows is running on my external drive, but installing the drivers is where my issue lies.

    When I run the setup app from my USB the setup seems to be going fine, and then the screen goes black. When I move my cursor to wake up the screen its really dim. If I let the setup finish it messes up my Windows install, so when I try to start up Windows again I just get the error status that it can’t boot, or something like that. When I look on my external drive the Windows files seem to still be there, but Windows won’t work.

    Does anyone have any ideas why installing the Bootcamp setup would do this?

  • I’ve done everything to the letter but still not working. My setup is below:
    Macbook Pro 2018
    OSX 10.14.4
    External Drive – OWC Express
    Drive in enclosure – Intel 320 Series SSD 300GB
    Cable for external drive – AmazonBasics USB Type-C to Micro-B 3.1 Gen2 Cable – 3 Feet (0.9 Meters)
    Here’s what I’m experiencing:

    1. Post VirtualBox installation and restart, I can’t only see the OSX Drive, EFI Boot but no windows
    2. Tinkering around in the Startup Utility gives me the Bless Tool issue (it is not a blessing)

    Any ideas for a fix?

    • It probably was the EFT boot drive. Mine at first didn’t say Windows. It said EFT Boot. Have you tried selecting that at boot to see what happens?

    • I’m having the same problem.
      MacBook Pro (15-inch, 2016)
      macOS 10.14.4
      External Drive – Delock External Enclosure For M.2 NVMe PCIe SSD – USB 3.1 Gen2 Type C
      Drive in enclosure – Intel SSD 660P 1.0TB M.2 80mm PCIe 3.0

      Here’s what I’m experiencing:
      1. Post VirtualBox installation and restart, I can’t only see the OSX Drive, EFI Boot but no windows

      I haven’t tried to select it in Startup Utility and boot.

      I’ll maybe try to do the installation on a normal PC and try the post installation on the Macbook.

      • Solution is to activate EFI in Virtualbox after you add the ISO. Then you click “Start.”
        Hit a key quickly before it gets to a powershell.
        Click through install as usual and click the custom install.
        Delete all your partitions.
        Click new.
        It should create 4 partitions including a EFI partition.
        Continue install.
        Quit install before restarting.
        Restart mac.
        Hit options key. Your drive should show up.