How to Fix Disk Layout Validation Failed for Disk 1 in Windows

If you’re trying to convert a disk from MBR to GPT using Microsoft’s MBR2GPT tool and see the error “Disk layout validation failed for disk 1”, it means the current partition layout doesn’t meet the tool’s conversion requirements. This guide explains why the error happens and the exact steps to fix it.

Why This Error Happens

mbr2gpt.exe is a Microsoft utility that converts a disk from the MBR (Master Boot Record) partition style to GPT (GUID Partition Table) without deleting data. However, it has strict requirements, and the disk layout validation step checks whether your disk meets them.

If validation fails, the conversion won’t proceed until those issues are resolved.

Common Causes of the Error

Several factors can trigger the disk layout validation failed message:

1. Not the system disk – MBR2GPT can only convert disks that contain the current Windows installation.
2. Too many primary partitions – MBR supports up to four primary partitions, but MBR2GPT requires three or fewer.
3. No active (boot) partition – The disk must have an active partition that contains boot files.
4. Unsupported Windows version – The tool works only on Windows 10 (version 1703 or later) and Windows 11, 64-bit editions.
5. Insufficient unallocated space – A small amount of free space is needed at both the start and end of the disk for GPT data structures.
6. Corrupted partition table – Damaged MBR metadata can prevent validation.

Step-by-Step Fixes: Disk Layout Validation Failed for Disk 1

1. Confirm You’re Targeting the Right Disk

First, make sure Disk 1 is your system (OS) disk.

• Press Win + X → Disk Management.
• Locate Disk 1 and check if it contains your Windows partition.

If it’s not your system disk, MBR2GPT will always fail.

2. Check the Partition Count

MBR2GPT requires three or fewer primary partitions.

• In Disk Management, count the number of primary partitions on Disk 1.
• If there are four, back up and delete or merge one partition.

3. Set the Active Partition

The active partition tells the BIOS where to load boot files from.

1. Open Command Prompt as Administrator.
2. Type:

diskpart
list disk
select disk 1
list partition
select partition X
active
exit

Replace X with the number of your Windows boot partition.

4. Free Up Required Space

MBR2GPT needs:

• 16 KB + 2 sectors of free space before the first partition
• 16 KB + 1 sector of free space at the end of the disk

If your disk is completely full, shrink the OS partition by 1–2 GB:

• Open Disk Management → Right-click OS partition → Shrink Volume.

5. Verify Windows Version

Run:

winver

If you’re on Windows 10 version 1703 or later (or Windows 11), you’re good. Otherwise, update before trying again.

6. Run MBR2GPT with the Right Command

In a full Windows environment, use:

mbr2gpt /convert /disk:1 /allowFullOS

From Windows PE, you can skip /allowFullOS.

Alternative Method: Use Third-Party Tools

If MBR2GPT still fails, consider tools that bypass its strict validation:

• EaseUS Partition Master
• AOMEI Partition Assistant
• MiniTool Partition Wizard

These allow MBR to GPT conversion without data loss and with more flexible requirements.

Quick Fixes

Cause	Fix
Not system disk	Target the OS disk
Too many primary partitions	Merge or delete partitions until ≤3
No active partition	Mark the OS partition as active
Unsupported Windows version	Update Windows
No unallocated space	Shrink partitions to create free space
Corrupted MBR	Repair with bootrec /fixmbr

The “Disk layout validation failed for disk 1” error is a safety feature to prevent conversion failures that could make your system unbootable. By checking partition count, disk type, active status, and free space, you can usually resolve it quickly. If you prefer a simpler approach, third-party disk management tools can handle the conversion without manual adjustments.