Can't install windows 10 on GPT? SOLVED

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valorouswon

Weaksauce
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Apr 30, 2014
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86
Hello,

I recently converted everything from MBR to GPT via diskpart in CMD (except for my current win7 ssd). Everything I've read about MBR and GPT says that GPT is newer and recommended for future compatibility with newer MOBOs. Now when I try to install windows 10 on my 3tb Seagate, I get this message. My BIOS is set to Legacy and UEFI so I'm not sure what the problem is here.

My current main windows 7 drive is a 840 pro, formatted as MBR, so when I turn to UEFI boot mode only I can't load it. I can't convert it back to MBR because then the partitians will be split, it needs to be GPT to have access to all 3tb.

I'm installing from CD (I know I know)

specs:

Seagate 3tb 7200
GA UD5 x79
3930k
Windows 10 Pro


Thanks!
 
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Realizing that I'm kind of screwed, because my current work drive is MBR, and my seagate is 3tb which can only use GPT to access the whole drive. So maybe I should just wait until projects over on october 2nd. I have to fresh install win 7 anyways and clone the drive for a backup.

But still, I feel there should be an option in Bios to have all drives working normally. Or, is my machine just too old?
 
You have to boot from the install media in EFI mode. Easiest way is to use your BIOS's boot menu.
 
I did switch EFI mode: Bios Bios Features - Boot mode selection - UEFI Only, also tried every other option in that section. When I boot in UEFI mode nothing happens, no bootable drive
 
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In the boot menu , there should be two entries for the drive, one for booting in EFI mode and the other for booting in classic BIOS mode. Select the EFI entry. This is easier than messing with the BIOS settings.
 
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Wouldn't hurt to set everything to legacy in the BIOS, then attempt to boot and if there is a TPM Module, you may have to clear that first.
 
Luke M said:
In the boot menu , there should be two entries for the drive, one for booting in EFI mode and the other for booting in classic BIOS mode. Select the EFI entry. This is easier than messing with the BIOS settings.
Click to expand...

I can't find this option

RandyG said:
Wouldn't hurt to set everything to legacy in the BIOS, then attempt to boot and if there is a TPM Module, you may have to clear that first.
Click to expand...

tried that, setting everthing to legacy and trying to select CD from bootmenu just ignores my selection and goes straight to windows
 
can you disconnect the win 7 ssd to see if it forces the 3TB as boot drive?
 
RandyG said:
can you disconnect the win 7 ssd to see if it forces the 3TB as boot drive?
Click to expand...

Yes I can get through now, but this still has nothing to do with GPT. MBR win 7 ssd is disconnected, everything set to legacy in bios, still saying can't be installed on GPT seagate
 
Luke M said:
In the boot menu , there should be two entries for the drive, one for booting in EFI mode and the other for booting in classic BIOS mode. Select the EFI entry. This is easier than messing with the BIOS settings.
Click to expand...

I remembetr seeing that some time ago, that option no longer exists
 
there are a lot of things working against you here. windows GPT support is bad at best. windows 10 64 bit must boot in native UEFI to support GPT. also i have NEVER had good luck with any conversion utility to convert a MBR disk to GPT, as windows implementation of GPT is outside of standards.

best bet, NEW Partition table, blank drive, disable all LEGACY bios options completely, and boot to a USB installer that has been configured to only allow UEFI boot.
 
the one provided by Microsoft works pretty good. I've yet to run into problems with the USB creation tool that Msft provides for Win10 and i've done probably 30 or so installs using them. Have yet to convert any MBR to GPT as I've always started fresh. Just didnt want to deal with the headache.
 
Zedicus said:
there are a lot of things working against you here. windows GPT support is bad at best. windows 10 64 bit must boot in native UEFI to support GPT. also i have NEVER had good luck with any conversion utility to convert a MBR disk to GPT, as windows implementation of GPT is outside of standards.

best bet, NEW Partition table, blank drive, disable all LEGACY bios options completely, and boot to a USB installer that has been configured to only allow UEFI boot.
Click to expand...

Seems like that might be the issue, the CD isn't UEFI, probably need a GUID partitian via USB. This isn't a big deal right now I'm just messing around, going to do a ful upgrade in a couple years but I wanted the 3tb for gaming drive.
 
valorouswon said:
Seems like that might be the issue, the CD isn't UEFI, probably need a GUID partitian via USB. This isn't a big deal right now I'm just messing around, going to do a ful upgrade in a couple years but I wanted the 3tb for gaming drive.
Click to expand...

its not actually the CD's fault, probably that the mainboard falls back to optical discs in legacy mode. no matter how much you kick a mainboard the division between what triggers BIOS and what will actually pass in UEFI is a pure headache. Even mainboards that have a UEFI/LEGACY only setting still do not usually actually work that way. how we are so far along and still have headaches caused by what is basically support for a floppydrive just boggles the mind.
 
valorouswon said:
SOLVED - using native UEFI flash drive. Bye bye DIscs

Thanks!
Click to expand...

Yes, that got me by surprise on my newest laptop build. A non-UEFI flashdrive install automatically formats for MBR on the system.

Microsoft has provided a non-destructive (although you should backup anyways) tool in Windows 10 to handle this.

**AGAIN, Backup if it's important, just to be sure**
CMD run as Administrator

diskpart
list disk
--> Get the disk 0 of the harddrive (if you have more than one, otherwise might not be necessary)
exit

MBR2GPT /validate /allowFullOS
... it should say that it is OK/confirmed. If it doesn't, make sure you don't have more than 3 partitions on the drive. MBR maxes at 4, and it needs to create a temporary one. So you'll need to drop a partition (I dropped the stupid HP Tools partition).

MBR2GPT /convert /allowFullOS
... should be done in a few seconds.


More here: https://docs.microsoft.com/en-us/windows/deployment/mbr-to-gpt


I had to do it with my laptop because I wanted to activate Bitlocker, but couldn't with MBR. My TSM required Secureboot+UEFI, so it'd fail. I realized this after I set everything up. Running the tool allowed me to save from having to reinstall everything.
 
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