Make an exFAT Bootable USB Flash Drive

Can you boot from an exFAT USB? Absolutely, but not by using a typical approach to USB booting. In order to make an exFAT bootable USB flash drive boot in UEFI mode, you will need to format the USB with multiple partitions. Then, install Grub2 on the boot partition. And finally, set your computer system to boot from the flash drive to confirm that it boots.

This process works for both Legacy BIOS and EFI booting. To be able to USB UEFI boot requires the creation of a second Fat/Fat32 partition, which is also covered in this segment.

Additional Notes: We will be creating an exFAT partition to be used for storing ISO files and for your traditional storage purposes. A second Fat32 BOOT partition will be created and used for Grub booting. Windows will only automatically assign a drive letter to the first partition. Which in turn, makes the fat32 boot partition natively hidden from Windows.

How can I view the hidden partition? You can use DiskMgmt to manually assign a drive letter to the hidden partition to make it accessible.

The advantage of using an exFAT partition over a fat32 filesystem for storing ISOs is that you can store bootable ISO files larger than 4GB, and still UEFI boot from them via the Fat32 boot partition. This is necessary because a Fat32 filesystem does not support storing file sizes beyond 4GB.

Caveats: Legacy BIOS booting does not work on a very small select few finicky CSM booted systems. Secure Boot is also not supported via this method.

The Diskpart version packaged with Microsoft Windows 7 and lower (Vista, XP, etc.) is not able to create multiple partitions on removable USB media. The process will fail to make the second partition. However Windows 11, 10, 8 should work fine.

On Linux systems, in order to exFAT format the first partition, the exFAT filesystem driver and utilities must be installed.

How to make an exFAT Bootable USB Flash Drive

Covered below are both Windows and Linux methods to make a USB boot from exFAT. Simply toggle to switch to the exFAT Bootable USB method you prefer to use.

Make a Grub2 exFAT Bootable USB Drive from Windows

I. Creating exFAT and fat32 Partitions on the USB drive

1. To get started, Open a Command Prompt as admin.
1.) From the Windows ‘⌕ Type here to search’ box, type cmd.exe
2.) Then click Run as administrator.
open command prompt as admin - cmd.exe
2. Type the following and press enter to launch Disk Management Tool.

diskmgmt.msc

Note which Disk and drive letter belong to your USB.
diskmgmt.msc - make an exFAT bootable USB
3. Back at the command prompt, type diskpart

diskpart

4. To select the disk, type the following replacing # with your USB disk number.

sel disk #

5. Then to wipe the disk, (WARNING: all existing content will be deleted) type the following one line at a time;

clean
convert mbr

6.  Next to list the disk info so we can set size in the next step, type;

list disk

And then note the size of your select * Disk in MB.
7. Now to prepare the first exFAT partition, type the following;

cre par pri
shrink minimum=50
format fs=exfat label=USB quick

8. Next to create and format the second partition as fat32, type;

cre par pri
format fs=fat32 label=BOOT quick
assign

9. Then, to verify the created partitions and volumes, type;

list par
list vol

IMPORTANT: note which drive letter was assigned to your fat32 BOOT partition. You’ll need it when installing Grub2.
10. To leave diskpart, type;

exit

II. Installing Grub2 for UEFI and BIOS on the USB drive

1. Download Grub2 from A1ive’s repository, and extract (using 7Zip) its contents to your Windows desktop.
Note: you’ll first need to extract the .tar file from the .gz, and then extract the contents of the .tar file. Once finished, you should have a grub folder containing the contents on your desktop.
2. Next to change to the grub directory, type or copy/paste the following;

cd %UserProfile%\Desktop\grub

3. To install Grub2 for BIOS and UEFI type or copy/paste the following,
(replacing X with your BOOT drive letter and # your Disk number),
and then press Enter.

grub-install.exe --force --no-floppy --target=i386-pc --boot-directory=X:\boot //./PHYSICALDRIVE#
grub-install.exe --force --removable --no-floppy --target=x86_64-efi --boot-directory=X:\boot --efi-directory=X:\
grub-install.exe --force --removable --no-floppy --target=i386-efi --boot-directory=X:\boot --efi-directory=X:\

Congratulations, you should have an exFAT bootable USB flash drive that is now able to Grub2 Boot from both Legacy BIOS and UEFI.

Upon completion, simply reboot your pc, select the USB drive from your BIOS or UEFI boot device menu, and then Boot. If all went well, you should be presented with Grub2!

Booting ISO files from an exFAT partition

Booting your select ISO files from a flash drive prepared as an exFAT bootable USB;

Grub can read from an exFAT filesystem using this method because it includes an exFAT driver module. However, to actually be able to boot from a Live ISO stored on the exFAT partition via loopback requires that the distribution also include a driver, and that the exFAT partition is automounted during boot. Otherwise, once the boot process has been handed over, the path to the ISO will no longer be found. When that happens, you’ll likely be dropped into a BusyBox shell.

Can I Boot ISO from USB without exFAT driver support?

Yes, there are a couple of ways to circumvent this requirement;

  1. Use PartNew to create and mount the ISO to a temporary partition.
  2. Or use map --mem to map the ISO to a memory address (if you have enough system memory).
  • Then, set the proper linux and initrd paths and proceed to boot the ISO.

This concludes the detailed procedure to create an exFAT bootable USB flash drive. Once I find the time, I plan to automate this functionality by adding the exFAT USB Boot feature to the YUMI Multiboot USB Software.