Happy Diwali Dear...
Yesterday night I have MBR booted to AIOBOOT through Grub4dos as default bootloader instead of Grub2 Legacy in my 32 GB GPT USB Drive. I have successfully booted to Windows 10 build 1903 x86/x64 ISO. I have also successfully MBR booted to Windows 8.1 Installer by using Grub4dos + NTBOOT combination.
Does Grub2 Legacy work for you if you test it in USB/HDD of size less than 2TB ? I think if your MBR boot to Grub4dos as default bootloader in your 3TB GPT HDD and then switch to Grub2 menu then it should work ?
You have to test following steps to see if Grub4dos -> Grub2 chainloading works for > 2TB HDD ?
1- Format 3TB HDD as GPT and create 30GB FAT32 GPT Partition for AIOBOOT. Note down Disk Number of your 3TB HDD from Disk Management. I have used Rufus for creating FAT32 GPT partition in my 32GB USB Drive. Let me know what method you use for GPT Partitioning of 3TB HDD ?
2- Download attached GPTgrldr.zip (All thanks to Wonko for this great concept) and move to C: Drive and extract as C:\GPTgrldr folder using 7-zip.
3-Open C:\GPTgrldr folder and choose File -> Open Windows PowerShell as Administrator option and type
Press Enter and type following command and press Enter. Where 3 is Disk number of your 3TB AIOBOOT HDD.
mkhidGPT.cmd myimage.img 3
Type YES to confirm, press [ENTER]. Grub4dos bootloader have been successfully installed in your GPT HDD...
4- Download attached NTBOOT.zip and extract all files in the root of your 3TB GPT HDD as follows.
5- Open AIO_Boot_Extractor.exe and choose your AIOBOOT FAT32 GPT Partition and press 'OK' button to extract all AIOBOOT files in the root of your AIOBOOT Partition of GPT HDD.
Note- Don't format your your GPT HDD here using AIOBOOT, Only extract AIOBOOT files using 'OK' button.
6- After extracting successfully it will Run AIOCreator.exe automatically, Click the Bootloaders button and install Clover.
7- Now copy following files from Windows 8.1 ISO to the root of AIOBOOT FAT32 GPT Partition.
8- Now also add latest Windows 10 Build 1903 x86/x64 ISO using AIOCreator.exe in your AIOBOOT GPT Partition..
1- Boot from 3TB GPT HDD in Legacy BIOS mode and choose AIOBOOT Grub4dos Menu option
2- Then select 'Load Grub 2' entry to open Grub2 Legacy menu and Select the WinPE & Setup menu to start the Windows installation. Perform the installation as usual.
Install Windows 10 on GPT partition Internal HDD using 3TB GPT USB-HDD in Legacy BIOS mode
You can also try to boot from your 3TB GPT HDD in Legacy BIOS mode and choose AIOBOOT Grub4dos Menu option and boot Clover from Grub4dos menu and choose to boot back to Grub2 (Grub2 will now be booted in UEFI mode). Select the WinPE & Setup menu to start the Windows installation. Perform the installation in GPT partitioned Internal HDD connected in BIOS/MBR based legacy system. The installer created the boot files during installation at this stage, waiting for the system to reboot. Boot into Clover but don’t select Grub2, select the Windows icon that the installer has created to continue the installation process.
Grub4dos + NTBOOT combiation to boot Windows 8.1 Installer from 3TB GPT HDD
If Grub2 legacy menu is still not working through Grub4dos chainloading in your 3TB GPT HDD then you can try following steps to boot Windows 8.1 Installer from your 3TB GPT USB-HDD using Grub4dos + NTBOOT combination.
Boot from your 3TB GPT HDD in Legacy BIOS mode and test both menu entries one by one-
1- NTBOOT TEST 1
2- NTBOOT TEST 2
Proceed till Disk Selection screen of Windows 8.1 Installer to see which entry allow your 3TB GPT to install Windows 8.1 in MBR/GPT Internal HDD of your system. You can test full Windows 8.1 Installation if have spare partition in Internal HDD.
Let me know if Grub2 legacy menu work for 3TB GPT HDD by using Grub4dos as default bootloader ?
Also test both NTBOOT menu entries to see if any work from your 3TB GPT HDD ?