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Exploring Win10 Clean Install Default Disk Layout

Last week, I posted a blog here about a sequence of DISKPART and other commands users can run to manually override Win10 default disk layout when performing a clean install. Like the material that follows here, it originated from friend and collaborator, Kari the Finn. I provide editing, color commentary, and additional background. In this follow-on post, you’ll find us exploring Win10 clean install default disk layout. We’ll show how it looks, and explain why it’s sub-optimal. In a follow-on post, we’ll provide the script one can use to automate this process.

Let’s Go Exploring Win10 Clean Install Default Disk Layout

As it’s installed on any UEFI / GPT machine, Windows 10 can automatically partition the disk. In that case, Win10 creates 4 partitions: recovery, EFI, Microsoft Reserved (MSR) and Windows partitions. No user activity is needed. One simply selects the target disk, and clicks Next. Windows automatically partitions the disk (assuming it’s blank and contains a single block of unallocated space).

However, we believe this automatic partitioning for a GPT disk is a bit off. Microsoft itself recommends the recovery partition be located after the C: partition in last place. Yet the company’s own automated Windows setup places it at the head of the disk as partition 1. This appears in yellow in the following screenshot. After that, three more partitions appear:

  • the EFI system partition (green)
  • MSR partition (not shown in Windows Disk Management and screenshot because it is hidden and unallocated
  • Windows partition (blue)

Exploring Win10 Clean Install Default Disk Layout

By default, the Recovery partition appears at the head of the boot/system disk. Even MS says it should take up last position at its tail.

Upgrades Pose Problems for the Default Layout

This default disk layout poses a problem any time you upgrade the machine. With each major upgrade from Vista to Windows 10, the recovery partition has increased in size. But when the default recovery partition needs more space it can’t take space from the EFI partition. That’s why a second recovery partition gets created after the Windows partition. This new recovery partition steals the necessary space from the Windows partition, reducing the OS partition to create the room it needs.

When you later add another Windows installation for dual boot you might end up with yet another recovery partition. Even so, this doesn’t ffect Windows functionality. It’s mostly an OCD kind of issue. But as old-school geeks, we prefer doing things right from the get-go.

This why we never let Windows setup partition our GPT disks. Instead, we partitioning those disk ourselves using a DISKPART script. That script places the recovery partition where it belongs, immediately following the C: partition. It adds less than a minute to total installation time yet provides this eminently preferable disk layout:

Exploring Win10 Clean Install Default Disk Layout

A sequence of DISKPART and other commands puts things in the proper order, with Recovery at the tail end of the boot/system disk.

What Makes the Recovery Partition Special?

The Windows Recovery partition on a GPT disk has a trait unique among all Windows partition types. Unlike all other types, a Recovery partition can expand “backwards.” That is, it can take additional space from the preceding partition. All other Windows partition types can only expand “forward.” That is, they can grab free unallocated space after them (shows up to the right in Disk Management and other partitioning programs such as MiniTool Partition Wizard). In sharp contrast, if the recovery partition is placed directly following the C: partition it shrinks C: when it needs more space for itself.

Here the same disk shown in the previous screenshot after uprading that PC to the latest Windows Insider build:

Exploring Win10 Clean Install Default Disk Layout

Placed properly the Recovery partition can grow itself as needed during the upgrade process.

As you can see, instead of creating an additional partition, the recovery partition grew 58 MB. The installer grabbed the space it needed for the upgrade (allowing a roll-back to the previous build) by shrinking C: and allocating that space to itself. This affords the additional benefit of maintaining the original disk layout, without having to switch to a new recovery partition and kiss off the space reserved for the original. Good stuff!

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