Booting from MBR NTFS formatted USB rescue media in UEFI mode


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Keith Weisshar
Keith Weisshar
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Why is my ASUS Z170 AMI UEFI BIOS able to boot from the MBR NTFS formatted USB rescue media in both BIOS and UEFI mode even though I formatted the flash drive as NTFS and created the USB rescue media with the Enable MBR/UEFI multiboot USB support disabled.  If I enable the Enable MBR/UEFI multiboot USB support option it gives a maximum number of partitions exceeded error message.  When I boot in BIOS mode there is no UEFI in the title bar.  When I boot in UEFI mode there is UEFI in title bar.
john.p
john.p
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Hi,

The UEFI standard mandates that the efi firmware needs only have support for reading FAT32 filesystems. Therefore, to ensure that any UEFI system will boot from a USB disk, the efi binaries must reside on a FAT32 partition. This will enable loading of Microsoft boot code that will then have enough support to read winload.efi, the kernel etc from NTFS to enable booting to continue.

When rescue media is created on USB media, the files required for UEFI booting are always copied and the function of the "Enable MBR/UEFI multiboot USB support" checkbox is only to ensure that they reside on a FAT32 partition. If there is enough space on the USB rescue media, a new FAT32 partition is created. The cause of your "max partitions" error is due to the fact that windows only supports one partition on usb flash media. On USB attached disks, this limit does not exist.

In your case unchecking the 'EFI multiboot' option allows the rescue media generation to proceed.on your flash stick. And as the firmware for your motherboard, unusually, does support NTFS, it will boot in EFI mode. You will find that this stick is not EFI bootable on most systems.

http://blogs.technet.com/b/askcore/archive/2013/03/20/creating-bootable-usb-drive-for-uefi-computers.aspx

I hope this clarifies matters.

Kind regards,
John.
w0w
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Keith Weisshar - 15 November 2015 12:35 PM
Why is my ASUS Z170 AMI UEFI BIOS able to boot from the MBR NTFS formatted USB rescue media in both BIOS and UEFI mode even though I formatted the flash drive as NTFS and created the USB rescue media with the Enable MBR/UEFI multiboot USB support disabled.  If I enable the Enable MBR/UEFI multiboot USB support option it gives a maximum number of partitions exceeded error message.  When I boot in BIOS mode there is no UEFI in the title bar.  When I boot in UEFI mode there is UEFI in title bar.

Create rescue.iso in Macrium and use it to create bootable USB NTFS disk with Rufus https://rufus.akeo.ie/
Just select proper USB disk, then ISO file and desired options like UEFI or UEFI CSM/MBR  boot mode and file system NTFS.
http://forum.macrium.com/uploads/images/e1965a1d-f2a7-41bb-8158-28f8.jpg

Edited 19 November 2015 7:31 PM by w0w
alternety
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I am also struggling with this. Among several other things.
I am having a problem following john.p
It seems to say that if you try to use a formatted and partitioned FAT32 USB stick to the Reflect builder of recovery devices,  you should not select UEFI check box, then the process will fail because it will attempt to build a second FAT partition. Is that what is really being said?



Nick
Nick
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Hi alternety

Thanks for posting

It seems to say that if you try to use a formatted and partitioned FAT32 USB stick to the Reflect builder of recovery devices,  you should not select UEFI check box, then the process will fail because it will attempt to build a second FAT partition. Is that what is really being said?


That's incorrect. If you select UEFI boot for your USB rescue media then the Rescue Media wizard will search for a FAT32 partition. If the USB flash drive is formatted FAT32 then this is fine. If a FAT32 partition cannot be found then an attempt to create an additional partition will fail on a Flash drive as Windows will only allow a single partition to be created on a flash drive by using Windows format commands.  The process is non-destructive as we don't want to destroy existing partitions and potentially lose data.

Please note that this thread discussion is concerning whether UEFI is able to boot from an NTFS partition on a Flash drive. As John has stated, this is not something that is part of the UEFI specification . Please see the extract below from Microsoft:   http://blogs.technet.com/b/askcore/archive/2013/03/20/creating-bootable-usb-drive-for-uefi-computers.aspx

UEFI based systems such as the Surface Pro  or other UEFI systems require that the boot files reside on FAT32 partition. If they are not FAT32 the system may not see the device as bootable.


And Wikipedia: https://en.wikipedia.org/wiki/EFI_System_partition

The EFI System partition needs to be formatted with a file system whose specification is maintained as part of the UEFI specification; the file system itself is based on the FAT file system but is independent from the original FAT specification


However, if your motherboard UEFI BIOS actually has support for reading NTFS, then by un-checking the option to enable UEFI support in the rescue media wizard, the USB stick may be able to boot in UEFI mode even if the Windows PE files are written to an NTFS file system.  We are still investigating which Motherboards support this and whether it is possible to detect BIOS compatibility with an NTFS UEFI system partition. We will do our best to ensure that Reflect is updated to make rescue media creation as painless as possible. 

Hope this clarifies

Kind Regards

Nick - Macrium Support

Edited 20 November 2015 12:47 AM by Nick
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