Convert Windows 10 from Legacy BIOS to UEFI without Data Loss  

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  1. Posts : 61,473
    64-bit Windows 11 Pro for Workstations
    Thread Starter
       #20

    gdc88 said:
    thank you all!!!
    @gdc88, were you able to convert to UEFI afterwards?
      My Computers


  2. Posts : 13,545
    Windows10
       #21

    Anibor said:
    I tried the conversion, got the error "Disk layout validation failed".

    Attachment 129730

    The computer has only one disk with two system partitions, a SRP boot partition and the Windows partition. Also an extended partition with two data partitions.
    I got this error initially. When I looked in the logs (used /logs switch) it turned out it was complaining it did not have enough space to write the new EFI partition. I shrunk the C drive by a few Gigs (overkill) and then it worked.
      My Computer


  3. Posts : 439
    Windows 10
       #22

    cereberus said:
    I got this error initially. When I looked in the logs (used /logs switch) it turned out it was complaining it did not have enough space to write the new EFI partition. I shrunk the C drive by a few Gigs (overkill) and then it worked.
    I looked at the logs. Initially, the extended partition was not recognized (?). I converted the two data partitions to primaries, and then the four partitions were recognized, but the problem you mention appeared:

    ValidateLayout: Too many MBR partitions found, no room to create EFI system partition.

    I suppose this is the normal situation, the procedure should handle these cases automatically. Otherwise it becomes a cumbersome trial-and error process, which involves manual manipulation of the partitions. Not good.
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  4. Posts : 16,278
    W10Prox64
       #23

    Navy is on the right track. I didn't suggest that because I am not so familiar with reagent and couldn't walk you through it. But there's a whole slew of problems like this on eightforums, when people had used EASEUS to modify partitions and then couldn't access the recovery partition.

    I would let Navy get your partitions in order with reagent.
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  5. Posts : 13,545
    Windows10
       #24

    Anibor said:
    I looked at the logs. Initially, the extended partition was not recognized (?). I converted the two data partitions to primaries, and then the four partitions were recognized, but the problem you mention appeared:

    ValidateLayout: Too many MBR partitions found, no room to create EFI system partition.

    I suppose this is the normal situation, the procedure should handle these cases automatically. Otherwise it becomes a cumbersome trial-and error process, which involves manual manipulation of the partitions. Not good.
    I know it does not delete the old system reserve partition. I wonder what would hapoen if you deleted it first.

    Anyway, I always delete recovery partitions as they are pretty useless in Windows 10 as you can use an installation drive to do the same thing anyway.
      My Computer


  6. Posts : 17,246
    Windows 11 Pro
       #25

    It sounds like this little utility is not quite up to prime time release. I would suggest that people try it once, and if it throws an error just use the manual method of converting if they still want to.
      My Computer


  7. Posts : 10
    windows 10 x64
       #26

    Brink said:
    @gdc88, were you able to convert to UEFI afterwards?

    YES:

    Convert Windows 10 from Legacy BIOS to UEFI without Data Loss-capture.jpg
      My Computer


  8. Posts : 13,545
    Windows10
       #27

    Some Tests Performed to understand how this works.

    Test 1 - MBR has 4 primary Partitions

    Convert Windows 10 from Legacy BIOS to UEFI without Data Loss-capture1.png

    Convert Windows 10 from Legacy BIOS to UEFI without Data Loss-capture2.png

    As expected, it failed to work. It is not clever enough to remove old SRP

    Test 2 - MBR has 3 primary Partitions but no unallocated space

    Convert Windows 10 from Legacy BIOS to UEFI without Data Loss-capture3.png

    Convert Windows 10 from Legacy BIOS to UEFI without Data Loss-capture4.png

    This validated fine - did not convert it.

    Test 3 - MBR had 4 Primary Partitions but SRP was deleted first

    Convert Windows 10 from Legacy BIOS to UEFI without Data Loss-capture5.pngConvert Windows 10 from Legacy BIOS to UEFI without Data Loss-capture6.png

    This worked fine!

    Convert Windows 10 from Legacy BIOS to UEFI without Data Loss-capture7.png

    Note how it shrank OS rather than look for unallocated space.

    Summary:

    1) You cannot use mbr2gpt if 4 MBR partitions to start with - from log you can see it creates EFI first then does conversion to GPT.

    (I do not see why it does not do conversion first then create EFI which would get round 4 MBR partition limit)

    2) You can delete SRP first to reduce MBR partitions to 3.

    Tutorial Recommendation


    Add sentence saying if drive already had 4 primary partitions, you need to delete the System Reserved Partition first

    Caveat: Not all MBR OS disks have an SRP for historical compatibility. Here it would be necessary to delete another primary partition eg a recovery partition


    Note: I do not know how logical partitions would work. More tests needed.
      My Computer


  9. Posts : 61,473
    64-bit Windows 11 Pro for Workstations
    Thread Starter
       #28

    I'd say if the tool fails, it may be best to clean install to UEFI instead.
      My Computers


  10. Posts : 17,246
    Windows 11 Pro
       #29

    cereberus said:
    Add sentence saying if drive already had 4 primary partitions, you need to delete the System Reserved Partition first
    Here's the problem, though....average Joe user deletes the System Reserved Partition and then the conversion to GPT and UEFI booting fails for another reason. Now what? Joe user is left with a computer that won't boot until one partition on that drive is made bootable again. My humble opinion is that it is dangerous for average Joe user to delete the System Reserved Partition their computer is booting from - at least without a major warning that deleting the partition will result in a failure to boot until either the conversion utility successfully creates an EFI System Partition or if it it fails another partition is made bootable.
      My Computer


 

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