Windows 10 - can be my UEFI and MBR conflict?

xxx123 · 27 Feb 2016

Hello. So this is my next topic but i am almost sure where is the problem. My ssd is Samsung Evo 250 GB.
At beggining time ,disk was formatted to MBR partition.
Problem started when some day i finished test in memtest86. Then after finished test i change booting priority in UEFI from USB to SSD.
After this Windows 10 started showing at 1 boot Automatic Repair and Diagnosing Pc. Windows 10 boot loader starts by "preparing automatic repair" and diagnosing pc.
Then after this i get screen with Your pc did not start correctly or Automatic Repair couldnt repair your pc . And when i click restart then Windows 10 boot fine. So i was needed 2 boots to boot properly to windows.
Disk was still on MBR partition.
Then i formatted disk using this time GPT partition. After this no problem with automatic repair, even if i am changing booting priority from USB to SSD ( tried many times ). Problem is not reproducable now.
So question is. It was propably issue with MBR and my UEFI ? MBR is not compatible with UEFI? Or maybe cause was other?

My ssd is Samsung Evo 250 GB , motherboard is Asus Sabertooth Z97 Mark 2, rams are 2x8gb Kingston Hyperx 1600mhz. Or maybe rams? I have read that some peoples resolved issue by new rams. But i doubt that rams was issue, because after format is now fine. What you think ?

Thank you.

Word Man · 27 Feb 2016

Legacy BIOS boot - MBR disk scheme / UEFI boot - GPT disk scheme. That's what's normally done with no problem. At least, that's what I think.

xxx123 · 27 Feb 2016

Maybe MBR get corrupted?

Word Man · 27 Feb 2016

I kind of doubt it. It doesn't make sense to me to expect the UEFI boot order to have any effect on a boot that you should have been doing in legacy BIOS mode if you have an MBR disk scheme.

If you tried to boot UEFI with an MBR disk - no go. You should have been trying to boot legacy BIOS (not UEFI) if you had an MBR disk scheme. Once you changed the disk to GPT scheme, of course (assuming the conversion included creating an EFI system partition) if should boot fine in UEFI.

xxx123 · 27 Feb 2016

So my motherboard is Asus SAbertooth Z97 Mark 2 with UEFI BIOS. I had previously installed windows 10 with MBR partition. So maybe that was reason of automatic repair loop? ( But like said on second boot it booted fine to windows 10 ) . Please answer. Thanks.

xxx123 · 27 Feb 2016

this:UEFI is the replacement for BIOS, and it's a relatively new thing in modern motherboards and OS's. It does things a bit differently than BIOS did, and sometimes there are strange edge conditions where a particular procedure will reliably cause unexpected behavior (like your process for making Windows 10 auto start it's repair system). So really, what you're looking at is a bug or "Feature" in the UEFI that doesn't behave the way Microsoft or the BIOS manufacturers expect. This exhibits itself in your strange boot behavior. In this case, I would expect it has something to do with maintaining compatibility with older OS's, and you have a conflict between UEFI and BIOS configurations. For example, your Motherboard might be trying to boot your SSD (HDD) using UEFI, and when you select the USB, you're selecting the NON-UEFI (aka BIOS) setting.

This means (likely) that on Shutdown, the OS tries to write something to the MBR (which doesn't exist, so it creates one), then on BOOT, the UEFI is looking for a GPT boot sector (or whatever GPT calls it) and gets confused because it finds a MBR (and a GPT too) instead. The OS then kicks in boot repair, fixes the GPT and off you go.

If you switch boot devices, try to keep them in the same family. If you use NON UEFI CD/HDD/SSD/USB on everything, don't switch any of them to UEFI or strange things may happen (and if you use UEFI don't switch to BIOS (aka Legacy).

Word Man · 27 Feb 2016

Took a spin through the manual for your motherboard - not clear to me if it can only boot UEFI or if there is legacy boot option or the equivalent thereof - if it can boot an MBR disk scheme, seems like you have to have the settings right to do that. No surprise, however, that you had no EUFI boot with an MBR disk - UEFI boot looks to EFI System Partition (which wouldn't be on your MBR disk scheme) or another inserted bootable device.

xxx123 · 28 Feb 2016

Word Man said:

Took a spin through the manual for your motherboard - not clear to me if it can only boot UEFI or if there is legacy boot option or the equivalent thereof - if it can boot an MBR disk scheme, seems like you have to have the settings right to do that. No surprise, however, that you had no EUFI boot with an MBR disk - UEFI boot looks to EFI System Partition (which wouldn't be on your MBR disk scheme) or another inserted bootable device.

So maybe that was reason of automatic repair loop? ( But like said on second boot it booted fine to windows 10 ) . Please answer. Thanks.

This means (likely) that on Shutdown, the OS tries to write something to the MBR (which doesn't exist, so it creates one), then on BOOT, the UEFI is looking for a GPT boot sector (or whatever GPT calls it) and gets confused because it finds a MBR (and a GPT too) instead. The OS then kicks in boot repair, fixes the GPT and off you go. Maybe because of this?

Word Man · 28 Feb 2016

I wouldn't have any way of knowing if your MBR disk was corrupted. How is it you were trying to boot an MBR disk with UEFI? What is "beginning time"? An MBR disk is not normally able to boot UEFI - although there is a trick to change boot partition (or system partition) to have UEFI boot files.

How relevant is your original question about MBR "corruption" if you've converted to GPT and all is OK? Are you looking to go back to MBR and still be able to boot UEFI?

xxx123 · 28 Feb 2016

After format is ok. No automatic repair. Even when i am changing USB to SDD is fine. But i am on GPT now.

I installed my Windows 10 in GPT partition. After this Windows 10 updated to new version and downloaded update.
In bios options i have SSD SAMSUNG and SSD SAMSUNG BOOT MANAGER. Why i have 2 boot of my ssd? What exactly it mean?

2 second question. So before format when i was booting from MBR partition had Automatic repair can you explain me why?