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I'm trying to convert my system to UEFI to get ready for the Windows 11 release. When trying to use the 'mbr2gpt /validate' command in cmd its telling me "Can Not Find OS Partition(s) for Disk 3"

Windows 10 is installed on Disk 3 (per Disk Management.. C Drive.. which is a M.2 drive in the motherboards M2[A] slot) And it shows as the "Boot" drive. However its not finding the OS.

Also, I'm not sure why, but Disk 1 (HDD) has a partition style of GPT, but there has never been an OS installed on that drive. It's only been used to store downloaded files, as that is what it was specifically bought for.

I have 3 other drives. One M.2 drive (for Games in Slot M2[B]) and 2 HDD, one for Programs and just a Spare Drive, which are just SATA drives

Screenshot of Disk Management and CMD

Marshall
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    What's really odd is that D: has the flag System... – Tom Yan Jun 29 '21 at 04:51
  • A disk can be GPT without any OS that isn’t what’s unusual about your system configuration. Your single partition on disk 3 is flagged to be active (thus you cannot use MBR2GPT) – Ramhound Jun 29 '21 at 09:31
  • Does this answer your question? Secure Boot / UEIF / WIndows 11 – Ramhound Jun 29 '21 at 09:32
  • @Ramhound right, but the concern was that 1 out of 5 drives say GPT but the rest, including the boot is MBR.. Makes not sense why when windows was installed on Disk 3 which it sets that to MBR then sets a completely empty drive to GPT. If a system is capable of UEFI/GPT it should default to that, not MBR. System, was built during pandemic shutdown. – Marshall Jun 29 '21 at 15:39
  • @Marshall - GPT incompatibility with legacy mode only exists with the system disk. If your system is using MBR, that means Windows was installed, while (Legacy or Combability) mode was enabled. Your system drive doesn't contain any of the partitions I normally would except from a MBR installation by the way. Drive 1 is likely GPT since it came that way, or simply due to it's size, there isn't any reason it should be MBR (the fact it's GPT isn't unusual). – Ramhound Jun 29 '21 at 15:44
  • @Ramhound the point being if the system is capable of newer functions, in this case UEFI/GPT then it should default to that, not legacy crap. All the hardware was brand new at time of build. 8 months ago.

    And the other posted question that you linked doesn't help at all. My issue is that the mbr2gpt is saying there is on OS on that drive, when there most certainly is.

    And the response to that question only gives information as to requirements. Makes no mention on how to resolve the discrepancy..

     – Marshall Jun 29 '21 at 16:45
  • @Marshall - The system is only using MBR due to the fact Windows was installed while legacy mode was enabled. You could use some other tool other than MBR2GPT to perform the conversion or determine which of the requirements your system does not satisfy for MBR2GPT. If I were to make an educated guess, it's probably the fact you have multiple disks flagged as active, yet none of them have the standard default partition that one might expect. That is a difficult problem, MBR2GPT making these checks, is preventing you from doing the conversion and then being unable to boot. – Ramhound Jun 29 '21 at 16:49

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