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

Verified 2026-10-282 min read

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

Tested onPro (26H2) · Build 26300.9457 · x64

Build: 26300.9457
Edition: Pro (26H2)
Architecture: x64
Support: Lab (clean install)
Evidence: E2Reproduced in the lab
Verified: 2026-10-28
Test machine: PVE VM 361; 256GB system disk; UEFI/GPT; clean install
Page type: Task

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

Boot the USB in UEFI mode.
Choose Custom: Install Windows only.
Select the unallocated space or delete the old partitions only after backing up.
Let Setup create the ESP/MSR/Windows/recovery layout.
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:

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.

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.