New NVME drive I installed with Windows became unbootable, pls help

I fixed it. It was very laborious but it worked. I'm going to describe the steps, in case someone else runs into a similar issue.

The idea came to me when I learned that you can actually shrink and expand volumes/partitions in Windows.

So, what was the problem at hand? All the special partitions (Recovery, EFI, MSR) were gone, I'm still not sure why, but it could be either AOMEI did this by error or me. What I had was just a plain volume that spanned almost the entire NVME drive, there was still a small leftover (Microsoft reserved space of 16MB) at the start of it. But that was useless, it's not enough to put all the bootloading files needed in the EFI partition. So I realised I needed some way to create some space at the start of the drive, before the partition where the Windows installation was. It was only the missing EFI that was making the Windows installed on the NVME drive fail to boot.

Since I only had 115GB of data on the NVME partition that hosted the Windows installation (out of a total space of 462GB), I realised I could just split the drive in chunks and just keep cloning the data from the beginning of the drive to the back of the drive, so to speak. By moving it on a partition that had an offset which started much "later" on the drive, I could create some unallocated space at the beginning of the drive.

But here's the trick. Windows does allow you to first shrink drives, which basically means you can split them into chunks, but if you later want to expand them to merge the pieces back together, it only allows this in one direction, while keeping the drive bootable: from the front to the back of the drive. If you try to expand a partition in the direction of the start of the drive, it will warn you this will create a dynamic disk and will not be bootable. And that's where the dilemma was. You have to both first move data to the back, to create space at the start, then have to move it back to the front, once you've created enough unallocated space at the front for the EFI and MSR, because you can only expand a drive from the front to the back if you want to keep it bootable. I used the AOMEI backupper free crap to move data around, by cloning those 115GB using this dynamic.

At the end of this operation, I finally managed to create about 5GB of unallocated space at the start of the NVME drive, which I could use to recreate the EFI and the MSR. I couldn't go lower than 5GB because that's the limit from the Disk Management tool.

You might be able to use this dynamic to create just enough space for the EFI and MSR from the command prompt outside Windows, since those tools might not have this limitation, but then you'd have to also do the data cloning, so have fun doing that outside Windows.

For the two last operations of actually creating the EFI and the MSR, I followed this tutorial, which is spot on:

https://zamarax.com/2021/02/10/how-to-restore-deleted-efi-system-partition-in-windows-10/

But you have to be careful, you need to pay attention to the assigned letters you have on your logical partitions, because it's likely they will differ from this tutorial. So make sure you select a partition in DISKPART then check its details with

detail partition

Also, that tutorial strings commands together, which my version of DISKPART rejected as syntax error. You might need to enter each command one by one, especially those that edit the bootloader entries using the bcdedit command.

If you follow these steps exactly and carefully, you'll be able to create a working EFI partition and boot your Windows drive, just like your were able to before something happened, which erased your EFI partition.

Disk Management shows that the HDD where I installed the current Windows (Disk 0) has a healthy EFI partition, but the NVME drive (Disk 2) doesn't.

I looked through the directory structure and it's mostly similar. It seems now Windows puts a Boot directory in /Windows and both the HDD and the NVME have this folder with boot files.

Maybe the only thing that's missing is that EFI partition chunk which I think it's used to load some drivers at boot.

Still looking at some tutorials that use BOOTREC/FIXMBR to fix the EFI bootloader, but I'm not sure why they involve an MBR, if these partitions are EFI and use GPT volumes.

Loner T wrote:

Assuming this is on a 2012 or older Tower MacPro, the missing EFI on NVMe is one possible reason.

If this is not on Mac, the GPT layout has an ESP, MSR and MSDATA. If you can install GPT Fdisk on the boot disk (running either Windows or macOS), we should check the GPT layout and determine the next logical step. If you are able to see NTFS file system on the NVME as indicated by the Windows Storage Manager, you are in a relatively safe place. AOMEI can be a bit off the mark, but GPT Fdisk should help us resurrect this beast.

On Diskpart, we should check which Volumes are on which disk. The UEFI_NTFS seems to be a small boot loader partition. Does it show any content in Windows explorer? We can also use GPT Fdisk for some of this.

Downloaded GPT Fdisk and extracted it. Not sure what could be installed here, seems to be a portable executable. I read the instructions and it says I should put it in a system directory included in PATH, so I put it in ./Windows/. Then if I launch it with Admin perms, I see this:

Not sure what's the next step here.

"AOMEI can be a bit off the mark"

Yeah, I only used it because I needed some tool that could erase a physical disk, not just partitions. And Windows just lacks the proper native tools to manage disks. But I had lots of issues with AOMEI and with another program usually recommended for cloning drives, like Macrium Reflect.

"The UEFI_NTFS seems to be a small boot loader partition. Does it show any content in Windows explorer?"

No, this partition is hidden, which is typical for recovery partitions. This is all I can see in Windows' File Explorer:

C: - HDD currently running the only bootable Windows, which I'm using to try to rescue the NVME installation.

D: - SSD on SATA, that used to hold the previous bootable Windows, which I erased and converted into a drive for storing documents that are used a lot, for fast access

E: - NVME drive on M.2 (running on PCIe 3, but I could also plug it into a PCIe 4 slot) - this had the bootable Windows which became unbootable after using AOMEI to erase the HDD drive and convert it to GPT.

Folder structure seems mostly similar on C and E, with just some small differences in how drivers were installed. So, I suppose the significant difference must be outside the logical drive itself, somewhere in the missing EFI/recovery partitions which were supposed to mediate the boot sequence.

Thanks for the help.

C:\Windows\gdisk>gdisk64.exe 0:
GPT fdisk (gdisk) version 1.0.7

The protective MBR's 0xEE partition is oversized! Auto-repairing.

Partition table scan:
  MBR: protective
  BSD: not present
  APM: not present
  GPT: present

Found valid GPT with protective MBR; using GPT.

Command (? for help):

Command (? for help): p
Disk 0:: 976773168 sectors, 465.8 GiB
Sector size (logical): 512 bytes
Disk identifier (GUID): 0D1F075D-5858-9090-8081-828310111213
Partition table holds up to 128 entries
Main partition table begins at sector 2 and ends at sector 33
First usable sector is 34, last usable sector is 976773134
Partitions will be aligned on 2048-sector boundaries
Total free space is 2029 sectors (1014.5 KiB)

Number  Start (sector)    End (sector)  Size       Code  Name
   1            2048         1085439   529.0 MiB   2700  Basic data partition
   2         1085440         1290239   100.0 MiB   EF00  EFI system partition
   3         1290240         1323007   16.0 MiB    0C01  Microsoft reserved ...
   4         1323008       976773119   465.1 GiB   0700  Basic data partition

Command (? for help):

Maybe I should just post the output on each disk.

Disk 0

Disk 0:: 976773168 sectors, 465.8 GiB
Sector size (logical): 512 bytes
Disk identifier (GUID): 0D1F075D-5858-9090-8081-828310111213
Partition table holds up to 128 entries
Main partition table begins at sector 2 and ends at sector 33
First usable sector is 34, last usable sector is 976773134
Partitions will be aligned on 2048-sector boundaries
Total free space is 2029 sectors (1014.5 KiB)

Number  Start (sector)    End (sector)  Size       Code  Name
   1            2048         1085439   529.0 MiB   2700  Basic data partition
   2         1085440         1290239   100.0 MiB   EF00  EFI system partition
   3         1290240         1323007   16.0 MiB    0C01  Microsoft reserved ...
   4         1323008       976773119   465.1 GiB   0700  Basic data partition

Disk 1

Disk 1:: 234441648 sectors, 111.8 GiB
Sector size (logical): 512 bytes
Disk identifier (GUID): 9D0257D3-5411-41EB-8D43-65E90A9C98BA
Partition table holds up to 128 entries
Main partition table begins at sector 2 and ends at sector 33
First usable sector is 34, last usable sector is 234441614
Partitions will be aligned on 2048-sector boundaries
Total free space is 2925 sectors (1.4 MiB)

Number  Start (sector)    End (sector)  Size       Code  Name
   1            2048       234440703   111.8 GiB   0700  Basic data partition

Disk 2

Disk 2:: 976773168 sectors, 465.8 GiB
Sector size (logical): 512 bytes
Disk identifier (GUID): CA2DB8B8-9552-4CB9-AB8F-7AEF6854AB9D
Partition table holds up to 128 entries
Main partition table begins at sector 2 and ends at sector 33
First usable sector is 34, last usable sector is 976773134
Partitions will be aligned on 2048-sector boundaries
Total free space is 2029 sectors (1014.5 KiB)

Number  Start (sector)    End (sector)  Size       Code  Name
   1            2048           34815   16.0 MiB    0C01  Microsoft reserved ...
   2           34816       976773119   465.7 GiB   0700  Basic data partition

I suppose the NVME drive is on disk 2, which is missing the EFI partition.

If I understand correctly, for the boot process to work, I need to manually recreate the EFI partition on the GPT NVME drive and restore the bootloader. But since there's only 16MB of unallocated space before the partition where the data from the Windows installation is, I probably have to use

bootrec /RebuildBCD

from a USB installer, via command prompt. Apparently the EFI partition itself should not be NTFS, it has to be FAT32.