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I want to upgrade my disk from MBR to GPT, and I tried using Windows' MBR2GPT.EXE tool to do the job. I used Windows' DISKPART tool to identify the disk I want to convert. However, this happened:

C:\WINDOWS\system32>MBR2GPT.EXE /convert /disk:0 /allowfullos

MBR2GPT will now attempt to convert disk 0.
If conversion is successful the disk can only be booted in GPT mode.
These changes cannot be undone!

MBR2GPT: Attempting to convert disk 0
MBR2GPT: Retrieving layout of disk
MBR2GPT: Validating layout, disk sector size is: 512 bytes
Disk layout validation failed for disk 0
MBR2GPT: Conversion failed

and the conversion failed. Using Diskpart again, I get the following output:

DISKPART> list disk

  Disk ###  Status         Size     Free     Dyn  Gpt
  --------  -------------  -------  -------  ---  ---
* Disk 0    Online          465 GB      0 B
  Disk 1    Online         3841 MB   960 KB

DISKPART> select disk 0

Disk 0 is now the selected disk.

DISKPART> list partition

  Partition ###  Type              Size     Offset
  -------------  ----------------  -------  -------
  Partition 1    Primary            100 MB  1024 KB
  Partition 2    Primary            464 GB   101 MB
  Partition 3    Recovery           813 MB   464 GB
  Partition 4    Recovery           511 MB   465 GB

Looking at the partitions on disk 0, there are 2 primary partitions and 2 hidden ones, I read here that the partitions might have something to do with the conversion failing, so I believe this is the culprit. If anyone could offer help converting my disk, that would be greatly appreciated.

2 Answers 2

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Hidden just means that the OS won't mount those partitions automatically. It isn't related to the success or failure of the conversion, since it's just a different value in the partition type field, the format of the partition is still the same

The MBR2GPT documentation says that in order to convert the drive to GPT all the following conditions must be met

  • The disk is currently using MBR
  • There is enough space not occupied by partitions to store the primary and secondary GPTs:
    • 16KB + 2 sectors at the front of the disk
    • 16KB + 1 sector at the end of the disk
  • There are at most 3 primary partitions in the MBR partition table
  • One of the partitions is set as active and is the system partition
  • The disk does not have any extended/logical partition
  • The BCD store on the system partition contains a default OS entry pointing to an OS partition
  • The volume IDs can be retrieved for each volume which has a drive letter assigned
  • All partitions on the disk are of MBR types recognized by Windows or has a mapping specified using the /map command-line option

https://docs.microsoft.com/en-us/windows/deployment/mbr-to-gpt

I'm not sure what type your recovery partitions are, but if they're both primary then you're out of luck. Another common issue is that there's no space left at the end of the drive for the backup GPT entries. In that case you need to resize the last partition to make space for them.

You can read Why does MBR2GPT conversion failed and how to fix? to see if it helps

But it's recommended to use a 3rd party solution, since Windows' built-in tools like diskmgmt.msc and mbr2gpt have very limited capability compared to external ones and can't solve complex situations. Some suggestions:

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  • 1
    As it happens, I have 4 partitions, two of them are primary. So that would explain that.
    – J-Cake
    Nov 24, 2018 at 7:38
  • What should I do if there is a logical partition in that disk? Jun 24, 2021 at 20:21
  • @AlirezaA2F if you have 3 partitions or less then just convert it to primary, otherwise just use a 3rd party software like I said at the end
    – phuclv
    Jun 25, 2021 at 0:17
0

My reluctance to purchase a third-party program for a one-use event set me on a mission to find the truth. After hours of research, I stumbled on a post by James Preston who figured out what mbr2gpt was actually doing and potentially why it failed.

For posterity (and in case his site ever goes down) I will copy/paste his suggestion here for all to see:

So after realising that my desktop PC has been running in BIOS mode (how 1970s and probably the result of multiple clones from HDD to 10k HDD, to 10k HDD in RAID0 to SSD and to another SSD) and with a free weekend I thought it was time to have a look at the MBR2GPT tool.

However in running the validate phase I was getting the error message:

"Disk layout validation failed for disk 0"

After following through a few red herrings on the internet I had a bit more of a dig into what the tool was up to and it appears that one of the first steps is to shrink the OS partition.

It appears that the fix is actually to preempt this and shrink the OS partition yourself (I reduced it by about 1GB – which made sense as one of the new partitions goes right in at the end of the disk), given these kinds of steps should only be performed by a person who knows what they are doing and understands the implications I won’t go into any detail as to how to do this other than providing the screenshot below.

Disk Management Screenshot

This personally worked for me, and I was finally able to overcome the UEFI boot requirement for Windows 11.

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  • Don't know why this was downvoted. But there's no need to purchase because there are lots of free 3rd party solutions out there
    – phuclv
    Sep 7, 2021 at 3:26

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