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I have a new MSI motherboard (UEFI), being used in UEFI+legacy mode, with two disks, one Ubuntu ( primary disk - GPT with bios_grub flag on ) and Windows 7 in the 2nd disk (MBR partition).

And I'm having trouble booting Win 7 from Grub2, ubuntu boots fine. If Windows 7 disk is the only one in the motherboard, it boots fine ( well after repairing it), but not in the two disk configuration. It's been days now searching all over, I've tried Boot-repair, I've edited the windows entry in the grub menu (using ntldr($root)/bootmgr) but no luck.

So my question is, is the ubuntu GPT partitioned disk an issue here, "confusing" Win 7, even though it is working in compatibility mode ( bios_grub flag on )? And how can I boot Win 7 from Grub2?




After much tinkering I found the culprit - one of the data disks (old IDE) uses an IDE->SATA converter which works only in MASTER Mode, (using a jumper on the converter itself), and this mode causes the Windows 7 (on another disk) to not boot, btw the motherboard has only SATA ports, no IDE. So I'm left with no options, either use this IDE disk or use Win 7, but not both. Whereas Ubuntu boots fine in any possible disks' configuration. So I might just go replace this IDE disk with another genuine SATA disk and be done with it.

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I booted XP on a MBR disk and various Ubuntu's from 10.10 to 12.04 on gpt drives without issue with old BIOS sytem.

Some BIOS have issues with drive mapping. Grub (and Windows?) consider the boot drive to be hd0 as that is from BIOS. When you chain load from grub it usually maps drives to make Windows then think it booted from hd0, even though it is hd1 from BIOS. But because of mapping issues, the only solution I have seen is to install grub to the MBR of the Windows drive. Then that drive is hd0 from BIOS and no mapping is required. Ubuntu will then boot just fine from other drive.

The new UEFI using a BIOS emulation mode just may not work with grub's old mapping.

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Thanks Oldfred, so it seems that I must install grub to the Windows disk (2nd disk - /dev/sdb in my case), not in the primary disk (/dev/sda), right ? I have to admit that the MSI's new UEFI bios has issues, so probably I just have to go that route then. – lind Sep 12 '13 at 21:28

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