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I am using my external HDD for backups, but for restore you need to boot into the specific software's "restore mode/utility" which is often an CD image, but I preffer to not use CD's and just use USB HDD's.

My HDD is formated into MBR, not GUID so it somehow won't boot until I switch my computer into legacy bios mode which does boot from MBR.

How can I boot from MBR when in EFI without legacy bios mode?

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I may be misunderstanding, but I get the impression that:

  • Your system's main hard disk is a GPT disk.
  • You're booting that disk in EFI mode.
  • You're using an MBR disk for backup purposes.
  • Your backup software includes a restore mode from an OS on the MBR disk.

If so, I recommend you contact the backup software's vendor for support. The problem is that some backup tools might not properly restore the EFI System Partition (ESP) from a BIOS-mode boot, so your backup might not work. If the vendor supports restoring from an EFI-mode boot, you should be able to convert your backup disk to GPT format, re-install your emergency OS in that mode, and use the system in that way. If not, you'll be taking chances on restore operations; it might work OK, but it might not.

You might be able to set up some systems to boot from your MBR disk in EFI mode, but my own experience with this is limited to Linux systems installed to USB flash drives. It's also possible to non-destructively convert MBR to GPT using tools like GPT fdisk, but this conversion will require re-installing the boot OS's boot loader. This process is easier with Linux than with Windows.

Knowing your OS and backup software might enable people here to provide more specific advice. Also, if I've misinterpreted your setup, please elaborate.

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interesting, +1, what linux software allows me to boot from USB+MBR? as long as I can get hirens boot CD to boot from MBR USB 3.0 I can restore backups safely –  Gizmo Aug 12 '13 at 21:17
    
USB+MBR is easy in BIOS mode -- any BIOS-mode boot loader for hard disks can be installed to a USB flash drive. If you meant "EFI+MBR," you should prepare the USB drive just as you would a GPT-based drive, but use MBR rather than GPT. Use a type code of 0xEF for the ESP. See my page on EFI boot loaders for general instructions. As a practical matter, though, there's little reason to do this; you can easily convert an MBR disk to GPT form, which is more conventional for EFI-mode booting and may work better on some computers. –  Rod Smith Aug 12 '13 at 23:42
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