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One of the keys to a successful Windows 10 upgrade process is getting the correct disk layout in terms of the order of the partitions.
The default order of the partitions in the Windows 10 disk layout actually runs contrary to what Microsoft recommends in its own documentation. In a fresh installation of Windows 10, the order of the partitions is the Recovery partition, the Extensible Firmware Interface (EFI) partition, the Microsoft Reserved (MSR) partition and the OS partition, as seen in Figure A.
Microsoft recommends, however, that the order be EFI, MSR, OS and then Recovery.
What is each partition?
The 450 MB Recovery partition -- NTFS in Figure A -- is where the Windows Recovery Environment (RE) is placed by default during the install process.
The 100 MB EFI partition -- FAT32 in Figure A -- for Unified Extensible Firmware Interface (UEFI)-based PCs is where the system stores the EFI files and data the OS uses during the boot process.
The 16 MB MSR partition -- Other in Figure A -- is the proprietary format and information reserved for Microsoft's exclusive use of Globally Unique Identifier Partition Table (GPT)-formatted disks. The OS does not make much use of the MSR except under special circumstances.
The OS partition gets the remaining drive space.
As an IT professional, you can switch the format to match Microsoft's recommendations, interrupting the Windows 10 upgrade process.
Why put the Windows RE partition last?
When the Windows RE partition follows the OS partition, the Windows Installer can automatically resize the Windows RE partition during the Windows 10 installation after the initial installation by stealing extra space from the end of the OS partition when it needs to grow. It's the only placement that allows for dynamic resizing during the Windows 10 upgrade process.
The Windows RE partition sizes have increased with each version of Windows. For Windows 8 and 8.1, for example, Windows RE was 200 MB. On Windows 10, it's 450 MB.
If you want to check the Windows RE partition on your current installation, open an administrative PowerShell or Command Prompt window and type the string reagentc /info. This will show you the Windows RE partition's status -- enabled or disabled -- its disk location, and the index for the partition in order of appearance, starting from 0.
In Figure B, which was taken from the same solid-state drive used to generate Figure A, you can see that the partition is identified as \partition1\ in the reagentc command's output.
Placing the Windows RE partition last on the disk next to the OS partition provides some assurance that subsequent updates won't add more recovery partitions to the disk layout. This is reason enough to interrupt the normal Windows 10 upgrade process to force this layout onto the OS target drive during a clean installation.
Boot from a USB drive or other media
You can create a bootable installer for Windows 10 using the Microsoft Media Creation Tool available through the company's Download Windows 10 page or use a tool such as Rufus along with a Windows 10 ISO file of your choosing.
Once you've built a bootable Windows 10 installer on a USB flash drive, you should:
- Make a backup of your system before proceeding any further. Be sure you have a rescue disk or other bootable media and can restore that backup if any problems arise. If anything goes wrong, you can boot from the rescue media and tell it to restore your backup.
- Use a diskpart script named right-disk.txt to automate the disk setup process. Copy it to the root of your bootable USB flash drive (UFD) or another USB flash drive that you'll insert in your target PC before you boot to the OS installer. You should copy it to that drive so you only have to work with one flash drive during the installation process.
- To begin the corrected install process, you must boot your target PC from the bootable flash drive. Insert the UFD, then click Start > Settings > Update & Security > Recovery > Advanced startup > Restart now button. Don't click Restart now until you're ready because it takes immediate effect.
- When the installer gets to the region and language selection screen, press the Shift and F10 keys to open a Command Prompt window.
- In the Command Prompt window, type diskpart, then press Enter to launch the disk partition command-line utility.
- Type list disk, then press Enter to list all the available disks. Note the number of the disk on which you'll install the OS. You should recognize it by its size and type. For most systems, this will be Disk 0, so that's how the subsequent commands are set up.
- Type list volume so you can see the volumes present on the target PC. Look for the drive letter for the UFD and the right-disk.txt script at its root. In most cases, this will be drive D:, as shown in the next command.
- Type exit so you can call the disk layout script you downloaded in step two. You must edit this script and replace the disk number that appears on line six -- change the 0 to the right number -- if you are installing Windows 10 to a disk with a number other than zero. Failure to make this change will destroy all the contents of Disk 0.
- Now, run the script with diskpart as follows: diskpart /s D:\right-disk.txt.
- Close the Command Prompt window when the script finishes running. You should be able to complete the normal Windows 10 upgrade process now by picking the proper language, your time and currency format, and the keyboard layout, and then clicking Next.
You should end up with a working Windows 10 installation and the disk layout in Figure D.
If something goes wrong during the Windows 10 upgrade process and the installation won't complete, use your backup to put things back the way they were.