# Windows 11 26H2 partitions: ESP, MSR, system, recovery and data

> Understand the UEFI/GPT partition layout Windows 11 creates, when to let Setup decide, and when manual partitioning is worth the risk.

**Tested on**

- Build: 26300.9457
- Edition: Pro (26H2)
- Architecture: x64
- Evidence: E2
- Verified: 2026-10-28
- Test machine: PVE VM 361; 256GB system disk; UEFI/GPT; clean install

## The short answer

On a UEFI/GPT system, Windows 11 creates a small **EFI System Partition (ESP)**, a **Microsoft Reserved (MSR)** partition, the **Windows partition**, and a **recovery** partition. The exact sizes are less important than the layout and boot mode.

For a normal single-boot PC, let Windows Setup create the layout. Manual partitioning is for dual boot, a separate data partition, or a disk you already planned. Do not delete a partition until you know what owns it.

## The layout you will see

| Partition | Typical role | Typical size | Format | Do not |
|---|---|---|---|---|
| EFI System Partition | Boot files, boot manager | ~100MB | FAT32 | Format it as NTFS |
| MSR | Reserved by Windows | ~16MB | None | Give it a drive letter |
| Windows | OS and apps | 64GB+; 200GB+ practical | NTFS | Fill it to 100% |
| Recovery | WinRE | ~500–750MB | NTFS | Delete it without a recovery plan |
| Data (optional) | Files, games, VMs | Remaining | NTFS/ReFS | Put the only copy of backups here |

Sizes vary by Windows build, OEM image and disk size. The table is a mental model, not a command to reproduce exact megabytes.

## Single boot: let Setup do it

1. Boot the USB in UEFI mode.
2. Choose **Custom: Install Windows only**.
3. Select the unallocated space or delete the old partitions **only after backing up**.
4. Let Setup create the ESP/MSR/Windows/recovery layout.
5. Do not create a second ESP on the same disk.

If Setup refuses to install to a GPT disk, check that the firmware is in UEFI mode and the USB was booted as UEFI, not Legacy/CSM.

## Manual partitioning: when it helps

- **Dual boot with Linux:** you need free space and a plan for the shared ESP.
- **Separate data partition:** useful for games, VMs or a second OS; not a backup.
- **Small system disk + large data disk:** keep the OS and user data separate, but back up both.
- **BitLocker:** the OS partition must be sized before encryption; resizing later is possible but adds risk.

### A safe manual layout

| Order | Partition | Size | Notes |
|---|---|---|---|
| 1 | ESP | 100–300MB | FAT32; shared with Linux if dual booting |
| 2 | MSR | 16MB | Windows creates it; do not assign a letter |
| 3 | Windows | 200GB+ | NTFS; leave 15–20% free |
| 4 | Recovery | 750MB–1GB | Put it after Windows |
| 5 | Data | Remaining | NTFS/ReFS; separate backup required |

Do not put the recovery partition before Windows unless you know your firmware and imaging tool can handle it. The default order is easier to recover.

## Disk numbers and destructive commands

`diskpart` is powerful and unforgiving:

```text
diskpart
list disk
select disk 1
detail disk
```

Only after confirming the disk identity should you run `clean`. `clean` removes every partition on the selected disk. There is no undo.

> **Danger: Check the disk number twice**
>
> In a laptop with an NVMe drive and a USB stick, Disk 0 is not always the internal drive. Use `detail disk` and the size/model to confirm. Unplug unnecessary USB storage before running destructive commands.

## After install

- Confirm the ESP is FAT32 and the Windows partition is NTFS.
- Check that WinRE is enabled: `reagentc /info`.
- Create a restore point or image before installing drivers.
- If you plan BitLocker, save the recovery key **before** enabling encryption.
- Do not move the recovery partition to “tidy up” unless you have tested recovery media.

## Lab note

VM 361 used a 256GB disk with the installer-created UEFI/GPT layout. The VM system disk is SATA because Setup could not see the VirtIO SCSI disk before drivers; that is a VM workaround, not a recommendation for physical hardware.

## Sources

- [Microsoft — UEFI/GPT-based hard drive partitions](https://learn.microsoft.com/en-us/windows-hardware/manufacture/desktop/configure-uefigpt-based-hard-drive-partitions)
- [Microsoft — Windows Setup: partition the disk](https://learn.microsoft.com/en-us/windows-hardware/manufacture/desktop/windows-setup-automation-overview)
- [Microsoft — BitLocker](https://learn.microsoft.com/en-us/windows/security/operating-system-security/data-protection/bitlocker/)

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Source: https://winbook.fyi/en/windows/install/partitions/