How to burn a USB stick for UEFI Windows 10 build when > 4 GB files are present

Making a USB stick for boot with large files

Some of the Windows 10 ISOs these days have files that are larger than 4 GB on them - I first found this with Fall Creators Update (FCU) and also useful tools like Media Creation Tool will sometimes fail. When I hit this problem I couldn't find much help for building USB images, as opposed to having imaging servers. So whether you've got your ISO from the Windows 10 download site or Visual Studio (replacing MSDN) then here's how you can sort it. NB You'll still need some form of license / activation of course.

The reason that building the ISO on USB for UEFI will fail as that UEFI can't read NTFS (which can have large files) but needs FAT32 which has a 4 GB file limit. This hit me on the Surface Pro 4 but in theory could be a problem with many machines.
  • Mount the ISO locally
  • Format a blank USB with FAT32 - needed for UEFI boot (can’t use NTFS)
  • copy all the files to the USB from the ISO. It will fail on copying install.wim into sources directory as > 4 GB which FAT32 doesn’t support. Say skip, rather than cancel
  • copy the install.wim from sources in ISO to a local directory
  • run the following command from an elevated command prompt in that local directory “Dism /Split-Image /ImageFile:install.wim /SWMFile:install.swm /FileSize:4000” - source article
  • this will create install.swm, install2.swm in the local directory
  • copy these to the USB in the sources directory
  • boot from the USB. E.g. on the SP4 you can get to USB boot by holding down volume down, and then touch power on. Keep holding until Surface logo appears. You can also get into the BIOS menu on SP4 if you do volume up, instead of down
NB Rufus may also work according to though I had issues - not sure if due to FCU, my machine or something else.


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