MBR-UEFI Issues

I am going to try to explain this the best I can. The version of Win10XPE I downloaded back in 2016 I used image 1803 to make my build. I took one TB USB drive and split it up into two partitions. One MBR NTFS and one FAT32 UEFI.

On the MBR partition I extracted the entire contents of the WinXPE ISO to that drive but only copied the UEFI folders and source folder from the ISO to the FAT32 partition. This created a Multi-Boot drive so to speak. When I would boot from a secure boot UEFI computer, the system would load the boot.wim from the UEFI partition but would find the CDUsb.y on the NTFS partition and make my NTFS drive letter Y:. This was perfect because all the stuff I needed was too big to fit on the FAT32 partition so this worked out perfectly.

The issue I am having now is I downloaded the newer Win10XPE and built my image with 1909. I did the same process of extracting the entire ISO to my NTFS drive and only the UEFI folders to my FAT32 drive but I am getting a huge error once everything boots into Win10XPE. I can still boot from a secure boot UEFI system but WinXPE will no longer locate the CDUsb.y on my NTFS drive so the NTFS drive no longer gets mapped as Y:\. If I use just a jumpdrive with the single FAT32 partition, the system finds the CDUsb.y and loads the USB drive as Y:\ but that isn't helping me any. If I boot the USB in just MBR mode, the Y: drive maps fine. For some reason the new stuff doesn't like the dual partitions. I also notice if you right click My PC and go to properties, it list which mode you have booted for the Model:. How is that determined on boot up to list UEFI Mode or MBR mode in system properties for Model:? The older 2016 version didn't do this. Below is some pics of how my drive is setup and was working fine this way until this newer Win10XPE version.     

MBR NTFS side



UEFI FAT32 side





I wish I could type the explanation out the way I see it in my head.

The version of Win10XPE I downloaded back in 2016 I used image 1803 to make my build.

I also notice if you right click My PC and go to properties, it list which mode you have booted for the Model:. How is that determined on boot up to list UEFI Mode or MBR mode in system properties for Model:? The older 2016 version didn't do this.

Win10XPE was first introduced in March 2018...

The version of Win10XPE I downloaded back in 2016 I used image 1803 to make my build.

I also notice if you right click My PC and go to properties, it list which mode you have booted for the Model:. How is that determined on boot up to list UEFI Mode or MBR mode in system properties for Model:? The older 2016 version didn't do this.

Win10XPE was first introduced in March 2018...

My apologizes. I was going by the modified date. The version that I used that I didn't have an issue booting from FAT32 and my drive letter from the NTFS was found as Y: I downloaded 11-15-18 and it's v1. I am now using v2 and having the issue listed in my original post. 

I assume you are using a 1TB USB external disk drive ...
I assume you require more then 32GB of partition space on your boot partition...
I assume you tricked the Fat32 Boot Partition to roll over into the Non-Boot NTFS Partition

XPE uses letterswap with the /Bootdrive switch and flag - from within pecmd.ini to assign the Y
I assume that due to your Multi-Partition setup - your BootPartition is not your Y partition

Code: [Select]

Test this Edit in pecmd.ini
> // LetterSwap
// EXEC =!%WinDir%\System32\LetterSwap.exe /auto /bootdrive Y:\CDUsb.y /Log %Temp%\LetterSwap.log

EXEC =!%WinDir%\System32\LetterSwap.exe /auto /SetLetter Y:\CDUsb.y /Log %Temp%\LetterSwap.log

Else you could use a 3rd party tool to format you Fat32 Partition larger then 32GB
Else you could setup you Drive to use a boot partition and a BCD with ramdisk option

I assume you are using a 1TB USB external disk drive ...
I assume you require more then 32GB of partition space on your boot partition...
I assume you tricked the Fat32 Boot Partition to roll over into the Non-Boot NTFS Partition

XPE uses letterswap with the /Bootdrive switch and flag - from within pecmd.ini to assign the Y
I assume that due to your Multi-Partition setup - your BootPartition is not your Y partition

Code: [Select]

Test this Edit in pecmd.ini
> // LetterSwap
// EXEC =!%WinDir%\System32\LetterSwap.exe /auto /bootdrive Y:\CDUsb.y /Log %Temp%\LetterSwap.log

EXEC =!%WinDir%\System32\LetterSwap.exe /auto /SetLetter Y:\CDUsb.y /Log %Temp%\LetterSwap.log

Else you could use a 3rd party tool to format you Fat32 Partition larger then 32GB
Else you could setup you Drive to use a boot partition and a BCD with ramdisk option

Thank you for the reply! The /SetLetter in the pecmd.ini did the trick! I didn't have to do that on my previous builds. I didn't do anything special, just formatted the drive with Partition Wizard. I appreciate your response. I don't mind adding /Setletter to the ini file. 

Thanks again!!

Well glad it worked for you.. 
I was unsure how letterswap works - but after reading the issue several times I was able to guess the cause...

If you make your "Edit" using the "Edit Pecmd.ini" on "Build Core" Main Interface
Your edit will carryover into every build...

Well glad it worked for you.. 
I was unsure how letterswap works - but after reading the issue several times I was able to guess the cause...

It just puzzles me why in v1 I did not have to change that line in the pecmd.ini to /SetLetter. I usually edit the pecmd.ini for my custom desktop shortcuts and such but I see I can do that from a cmd on the root of the drive with v2. I will for sure change that setting in the ini before I make my build from here out.

I really appreciate your time on this!

Somewhere along the way the process used was changed...

Somewhere along the way the process used was changed...

I suppose so but I am glad you pointed me to a workaround! 

Good to have found the right switch for multiple partitions 

I didn't look at Nikzzzz's source to see the difference between
/bootdrive Y:\CDUsb.y   and   /SetLetter Y:\CDUsb.y
But I suppose /SetLetter is sufficient and good for the different cases, simple or multi patition(s) usb stick/disk.
And Probably good to have it in pecmd.ini as default value

LetterSwap.exe has changed http://theoven.org/index.php?topic=93.msg31477#msg31477 . Maybe the reason it worked before for you laddanator

Good to have found the right switch for multiple partitions 

I didn't look at Nikzzzz's source to see the difference between
/bootdrive Y:\CDUsb.y   and   /SetLetter Y:\CDUsb.y
But I suppose /SetLetter is sufficient and good for the different cases, simple or multi patition(s) usb stick/disk.
And Probably good to have it in pecmd.ini as default value

LetterSwap.exe has changed http://theoven.org/index.php?topic=93.msg31477#msg31477 . Maybe the reason it worked before for you laddanator

Makes complete sense now! I do think setting that \SetLetter would not be a bad idea to set as default in pecmd.ini file. I have set it to default in my builds now. That would pretty much cover almost any type or regular boot or multi-boot situation.

Thank for all that you guys do on this project! Will be sending some Christmas funds to you guys shortly.