How to run Bootcamp and Windows 10 on a USB SSD

I’ve been using a late 2013 Retina Macbook Pro as my primary computer for almost two years. It meets all my needs in my day job and is light enough to carry everywhere even while flying around for work.

While I love the time flying affords to switch offline and catch up on some well deserved gaming, mobile gaming can be bit bland and Mac OS X doesn’t run my favourite games like Skyrim without some fairly unreliable and poorly performing hacks via Wine.

But what about Bootcamp? I was in a very limited place, the 256GB SSD quickly fills up and I couldn’t spare the space to partition and install Bootcamp Apple’s way.

Enter the Samsung Portable SSD T1, this speedy little drive is small enough to hang off the side of my Macbook without getting in the way and a bump or two won’t damage it.

Unfortunately Windows refuses to install to any USB based storage which has historically been far too slow to run a fully fledged operating system.

But that’s no issue for the T1 which by Samsung’s own estimates can reach up to 450MB/s. It’s more than fast enough to run Windows as if it were running directly on the internal drive.

Luckily with the power of virtualisation it’s easy to bypass these pesky limitations and get Bootcamp running entirely off the external USB SSD drive without making any changes to the internal SSD.

Read on to find out how!

What you’ll need:

You’ll need a few things to complete this guide:

• A Mac which supports booting from a USB Device (see Apple Support: Mac computers that support Windows 10)
• A USB 3.0 SSD similar to the Samsung T1 (a flash storage device will not be fast enough)
• A spare USB drive with a minimum of 2GB of storage to copy the Bootcamp Drivers over to Windows.
• Basic understanding of VirtualBox and installing Windows.

Download Windows 10 Installation

Windows 10 is available to download from Microsoft and allows a grace period to license the installation. Windows 10 can be purchased from the Microsoft Store.

Click here to access the Windows 10 download page.

Follow the prompts to download Windows 10 installation disk.

The download is 3.7GB so it may take some time, the next steps will prepare your system to install Windows 10 to the USB SSD.

Download Bootcamp Software for Windows 10

Apple offer a prepackaged driver installation for Bootcamp.

Click here to download the Bootcamp 6.0 drivers for Windows 10 via the Apple CDN. (AppleBCUpdate.exe 1.13GB)

Thanks to Reddit user sadalhayat for identifying this link.

Once this has downloaded copy it to a spare USB drive separate from SSD you will be using to install Bootcamp. Save this for later.

Mac OS X cannot write to the Windows drive out of the box. For this reason you will need to use a separate drive to copy the Bootcamp Software into the new Bootcamp Installation.

Install VirtualBox

Are you wondering why VirtualBox is the next step? Don’t worry, we’re taking advantage of the virtualisation technology to kick start the installation of Windows 10.

We will be using VirtualBox to mount the USB drive as a virtual hard disk inside the Virtual Machine. This bypasses the limitations imposed by the Microsoft Installer preventing us from installing Bootcamp the Apple way.

Download and Install VirtualBox

If you don’t already have VirtualBox, it can be downloaded from their website. Once you have downloaded the package, use the installation package to get up and running with VirtualBox.

Identify your USB Drive’s device location

Open up the Terminal and type:

diskutil list

This command will list all the connected drives on your computer. Browse through the list until you find your storage device.

Your result will look similar to this. Read over the type names until you find one that is your USB SSD.

The text highlighted red “/dev/disk2” is the information we need. This information will tell VirtualBox exactly which storage device it needs to access.

Please note this information may be different on your machine. Read the list carefully to match the address of your USB SSD.

Disconnecting Mac OS X from the USB SSD.

Before we connect VirtualBox to our USB SSD you will need to completely unmount the SSD from Mac OS X to allow VirtualBox full access to the USB SSD.

This can be done by searching for Disk Utility in Spotlight then

1. Choosing the External USB Device
2. Choosing Eject in the top Menu

Create a Virtual Disk mapping to the USB Drive

This is where the magic starts. We will be using VirtualBox to mount the USB SSD as a normal hard disk in order to trick the Windows 10 installer into thinking it is using a normal hard drive.

First we need to create a Virtual Disk File for VirtualBox so it knows what storage device we are accessing.

Below is the command we will be modifying to create the Virtual Disk file

VBoxManage internalcommands createrawvmdk -filename "bootcamp.vmdk" -rawdisk /dev/diskX

You can copy the entire command with the exception of the last part “/dev/diskX” which will need to be changed to the drive number you identified in the previous step.

In my case it is “/dev/disk2”.

Installing Windows 10 to the USB SSD via VirtualBox

Now that we have everything organised we can start the installation of Windows 10 via VirtualBox.

We will need to give VirtualBox elevated permissions to access our handy bootcamp.vmdk file.

In your terminal type:

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

This will force VirtualBox to run as the root user and have permission to access the USB SSD.

Creating Virtual Machine

In VirtualBox choose “New” and type “Windows 10 Bootcamp” and click Continue.

Change Memory to “512” MB and click Continue.

On the Hard Disk screen choose “Use an existing virtual hard disk file” browse to your home directory and select the newly created “bootstrap.vmdk”.

Installing Bootcamp, from a Virtual Machine

Now that we have scaffolded the Virtual Machine, connected the hard drive and downloaded Windows 10, it is time to install Windows 10 onto our shiny new USB SSD.

Back in VirtualBox we will need to mount the Windows 10 Installation ISO into the virtual DVD drive.

1. Open the Virtual Machine’s Settings Panel.
2. Select the Storage tab on the top of the Settings Panel.
3. Select the Empty DVD Icon.
4. Select the CD Icon next to the Optical Drive, Choose Virtual Optical Disk File and select the Windows 10 ISO file.
5. Select OK to save the new settings.

Run the Normal Windows 10 Installation

Follow through the standard screens to begin the Windows 10 installation.

Clicking next and agreeing to the terms and conditions is all you really need to do here except for the following points:

When you meet the installation type screen, select “Custom”.

Delete exisitn

When you are asked where to install Windows, just delete any existing partitions and select “Next”.

Don’t worry, Windows can only see the USB SSD drive you assigned by VirtualBox, your Mac’s existing partitions are not accessible here.

Important! Don’t let windows restart!

Important! Don’t let windows restart! This is the most crucial step.

This is the most crucial step to successfully installing Bootcamp on an external USB 3.0 SSD

Power off the Virtual Machine

When Windows 10 is restarting, make sure you prevent Windows restarting inside the Virtual Machine and completing the installation.

1. When you see the VirtualBox BIOS screen select the Red Close Button
2. Choose “Power off the machine”.
3. Choose OK to power off the Virtual Machine.

That’s enough Virtualisation!

Now that we’ve completed the first phase of the Windows 10 installation, we don’t need to use VirtualBox anymore.

This completes all the steps required on the Mac OS X side of the installation.

Reboot your Mac into Windows

It’s now time to restart your Mac and boot into Windows 10. Power off your Mac and hold the Option key until disk icons appear onscreen.

For more info see Apple Support: Select an operating system while starting up your computer

Let Windows 10 install

If everything went well Windows 10 should start booting and begin the initial installation.

Just follow through the screens and fill in your details as required.

Windows 10 may reboot during the installation. If this occurs, make sure you press the Option Key and select the Boot Camp Drive to continue the installation.

Install Bootcamp Software

Plug in the spare USB Drive we copied the Bootcamp Software to earlier and run “AppleBCUpdate.exe”.

This will start the Bootcamp installation software to install drivers for the Apple Keyboard and Mouse, Wireless, Graphics and other devices in your system.

That’s it!

If everything went according to plan you should now be able to boot directly into Windows 10 whenever the USB SSD is connected to your computer!

My experience has been rock solid, and I can enjoy all the benefits of running Bootcamp on my Mac to run Windows Applications and Games without sacrificing the valuable storage space of the internal SSD.

Did you find this article helpful? Let me know in the comments section below!

Keep in mind Microsoft and Apple never intended for you to run Bootcamp this way. Make sure you never disconnect the USB SSD from your system while Windows is running!