win10-install-to-external-hdd-using-winpe.md

Installing Windows 10 to an external drive without a Windows host

The long story

We were talking at the office about having a LAN Party and playing some old school games like Age of Empires and Starcraft. The issue is that I have Linux installed. I didn't want to ruin everyone else's fun by having random crashes, out-of-sync errors and similar stuff using Wine, and I didn't want to do the dual boot dance, so I figured out that the best option was to install Windows to an external drive.

I remember that something called Windows To Go existed a while ago, but it was restricted to Enterprise versions. Eventually I found out that creating a Windows To Go drive is a really straightforward process:

1. Partition the External Drive and format it as NTFS.
2. Expand the Windows image using dism.
3. Install BOOTMGR using bcdboot.
4. Boot from the External Drive and continue the setup.

The process was so straightforward that I tried to do everything from the Linux side, but I encountered some issues and eventually gave up. It may actually be doable, because the issues were small:

1. You need to compile the edge version of ntfs-3g, and build wimlib (linux alternative to dism) linking it against the edge version of ntfs-3g in order to expand Windows 10 images. Source.

2. There isn't a tool like bcdboot for Linux, so you need to install BOOTMGR manually.

In the end, I decided to do everything from WinPE and the most straightforward way to use WinPE is to boot into the Windows Setup.

The actual steps

1. Download the ISO from the official website.

2. Boot into the Windows Setup and open the Command Prompt with Shift + F10.

   This step is intentionally left ambiguous. There are too many many ways to boot into the Windows Setup. You can create a bootable USB, burn a DVD, you can also mount the ISO and your external disk in VirtualBox.

   This article will use the VirtualBox approach, you can check the instructions to mount your external disk here.

3. Run diskpart to partition and format the disk.

   list disk                           // list every disk and their number
   select disk 0                       // change 0 with the # you wish to use
   clean
   create partition primary size=512
   format fs=fat32 quick label=BOOT
   active
   assign
   create partition primary
   format fs=ntfs quick label=Windows
   assign
   list volume                         // you'll need the drive letters later
   exit
   

   These steps will create an MBR layout in the disk and a boot partition, this is intentional to achieve compatibility with both firmwares: BIOS and UEFI.

   In this example, the C drive is the BOOT partition, the D drive is the Windows Setup DVD, and the E drive is the Windows partition. The drives in your PC will probably be different, so you'll need to update the instructions for your particular configuration.

4. You'll need the find the index of the edition of Windows you wish to install using dism. Remember to adjust the /imagefile: argument if required:

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

5. Proceed to expand the Windows image with dism, in this example I'll be installing Windows 10 Pro, which is the 6th index. Remember to adjust the /imagefile:, /index: and /applydir: arguments if required:

   dism /apply-image /imagefile:D:\sources\install.wim /index:6 /applydir:E:\
   

6. Install BOOTMGR to the external drive. Remember to adjust the arguments if required; In this example I'm telling bcdboot that Windows was expanded to E:\Windows and that it should install the bootloader in C:; the /f ALL argument installs both UEFI and BIOS bootloaders:

   bcdboot E:\Windows /s C: /f ALL
   

7. Hide the BOOT partition using diskpart.

   list volume
   select volume 1                     // select the `BOOT` volume
   set id=1c                           // `1c` is Hidden FAT32 (LBA)
   exit
   

8. Finally, turn off the VM, plug the external drive to your PC and continue the Windows Setup. It will proceed to install the drivers and apply the initial configuration.

You, sir, are a lifesaver... Works great! Modern USB3 flash drives are about as speedy as regular SSDs.

I run zero physical Windows machines, so it helps to keep one of these around on the off chance I need to do something through "legit" Windows.

Link update: https://www.serverwatch.com/guides/using-a-physical-hard-drive-with-a-virtualbox-vm/