Why does Win 10 Enterprise x64 21H2 insist on creating an extra EFI partition at end, even when there's already one ?

[Mrx]

As per title...

I have used TBEXPLO to pre-partition my disk as follows:

260MiB EFI System partition
16MiB MSP/MSR partition
100 GiB C: Windows partition (NTFS)
1 GiB WinRE Windows Recovery partition
1 MiB Free Space (Needed after WinRE, otherwise Windows will shrink C: and create an extra WinRE after C:, with 1MiB Free Space after it, before the already existing 1 GiB WinRE partition)
1 TiB D: DATA partition (NTFS)
150MiB IFL Recovery partition (FAT-32)
186GiB Free Space to end for Over-provisioning

Why does Win 10 Enterprise x64 21H2 insist on creating another 100 MiB EFI partition at end, rather than using the existing one at the beginning of disk ?

On the partition selection window at beginning of Windows installer setup, after selecting C:, the installer complains that the partition layout is not correct for GPT, and to check microsoft.com. Any ideas why ?

[Mrx]

Also, on every subsequent install of Windows without changing previous partition layout, Setup will create another EFI partition every time in the free space near the end. Again, even if it doesn't like the original one at the start of disk, why doesn't it at least use the EFI partition that it created itself on the previous install ?

[TeraByte Support]

did you actually create it as an EFI System partition (and it's formatted)? It's a special type, you can use properties to check / change the type.

[Mrx]

I created all partitions in TBOSDTS TBEXPLO tool. Didn't format them. Did this multiple times in both in Windows version of TBEXPLO tool, and also IFL's version (no formatting), and it still created another EFI partition at end.

After you mentioning to format them, I hadn't, but tried that in Partition work (in IFL) and still same issue with it creating another EFI partition, when one alreay exists as first partition on disk.

Next thing I'm about to try is create EFI partition in TBEXPLO, but then during Win Setup/Install, on PArtition selection dialog (ie. where to install Windows), I'm going to try formatting it there, then install to Empty space (then try to existing NTFS partition) for C:/Win install, to see if that works.

[TeraByte Support]

check to ensure it's an efi system partition "type" not just name.

[Mrx]

Already done that - As mentioned I created all partitions in TBEXPLO OSDT, in both Windows and in IFL - Always same result - An extra EFI partition is created at end.

Steps to reproduce on my machine, with the two SSD's are...

1. Boot Windows 10 22H2 (all updates) on Western Digital SSD (Target 2nd Win install disk is Samsung SSD - should be irrelevant, but...)

2. Launch TBEXPLO and create previously mentioned partition layout, in order as shown below (NOTE: TBEXPLO creates EFI as 100MiB, which I immediately resize to 260MiB, I also create WinRE partition of size 2GiB, as while tesing my Win install ISO (which had a lot of drivers integrated - including to boot.wim, whoich is the WinRE image), Setup would created another WinRE partition, if existing one was not large enough - which is expected)

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260MiB EFI System partition
16MiB MSP/MSR partition
100 GiB C: Windows partition (NTFS)
1 GiB WinRE Windows Recovery partition
1 MiB Free Space (Needed after WinRE, otherwise Windows will shrink C: and create an extra WinRE after C:, with 1MiB Free Space after it, before the already existing 1 GiB WinRE partition)
1 TiB D: DATA partition (NTFS)
150MiB IFL Recovery partition (FAT-32)
186GiB Free Space to end for Over-provisioning

3. (Because you mentioned about formatting, I did this step to make sure) - Boot into IFL > Partiton Work and format the EFI, MSR, WinRE partitions.

4. Boot into Win 10 21H2 Initial ISO (Yes, host Win is 22H2 with all updates, but test install ISO to Samsung SSD is 21H2 - again, should be irrelevant, but..) to install to 100 GiB C: partition (ie. original Nov 2021 release ISO)

5a. Win Install Setup partition, "Which partition do you want to install to ?" dialog is shown

5b. I choose the 100 GiB C: partition, click Next button, and a dialog is displayed saying "The partitions on the disk selected for installation are not in the recommended orde. For additional information.... Check out MS website for more info on installing to GPT. Do you want to continue ?"

5c. I click OK/Yes to continue

6. Installs Windows fine, but when I check partition structure, an extra EFI 100 MiB partition has been created in 186GiB free space at end of disk.


** NOTE: This is in VirtualBox VM, but it also happens on real install (Wait for me to re-check the real install part, but I wanted to get information down - aside from that check I need to make, an extra EFI partition is ALWAYS created after IFL partition (it doesn't shrink the IFL partition), in 186Gib Free space at end).


Are you unable to reproduce it ?


NOTE FOR SELF: Try..

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- Not resizing EFI partition from intial 100 MiB to 260 Mib ?
- Keep it EFI partition at 260 MiB, but Format it Win Setup install partition selection dialog (ie. let Windows Setup format EFI partition)

- Post back here with results