Converting MBR to GPT


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I have windows 10 Pro V.1803 installed on a SSD, and have discovered that I can't reinstall Windows, as the drive is in MBR format.

I'm going to have a go at converting the drive to GPT using the MBR2GPT.exe utility in Windows. Apparently it retains all files, so hopefully works well. Just in case, I have an image disk of my SSD I can restore with Macrium Reflect.

I understand from reading and watching a tutorial that I will need to update the bios after conversion to GPT, so that the disk boots as UEFI.

I've not edited the bios before, so just want to check I'll be editing the correct setting! Here's a screenshot of my current bios settings.


Is it the Storage Boot Option Control that I need to change from Legacy to UEFI ?

I hope someone can confirm.

Myles
 
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It might be good to attach a Disk Management picture of your current install.

The one time I ran MRB2GPT is worked OK.

Are you wanting to change to UEFI for some specific reason?

If you are installing, by removing all the partitions, the install will covert the drive to GPT if you boot the install media as UEFI.

On your attachment, I would say the highlighted entry needs to show Legacy or UEFI but Bioses vary so greatly, depending on the age of the system, it is hard to know for sure. The Windows 810 Features entry may need to show Windows and not Other OS. In some cases, enabling Secure Boot sets the system up for UEFI only. You need to boot into a Windows Boot Manager and not a specific drive if you have an option in the Bios or a Boot Device Menu.
 
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@Saltgrass, thanks for your reply. Here's a pic of my disk management -



It doesn't seem to show the status of disks as far as MBR and GPT, but Macrium does! Here's their results -



My SSD is MBR, my second drive is GPT and my third drive is MBR.

I want to change to UEFI because at some point I want to do a fresh install of Windows. However, Windows 10 refuses to install on MBR and states disk has to be GPT.

My machine is only a couple of years old - with a MB-531-GI Gigabyte GA-Z170-HD3P Intel Z170 (Socket 1151) DDR4 ATX Motherboard.
 
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Are you sure you want to install Win 10 on such a small SSD? It may be legal but the way Win 10 updates are done, sometimes you need much more room than you would think. I would go for at least a 500 GB drive to make sure you are not going to be limited later.

The MBR2GPT software will place a UEFI partition on the drive, after the C partition. After that process you should be able to change your Bios although when I changed mine, it was already set to boot into UEFI.

If you have system images of your install then you are pretty much protected, but to do a clean install of Win 10 you could just wipe the SSD (or remove the partitions during the install) and install as UEFI..
 
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Why not install Win 10 on a 120GB drive?? Myself I have two systems on a 120GB drive, Windows 7 AND Windows 10. My Windows 10 partition never goes over 30GB, although I have my files (documents,pictures etc.) on drive D: which is an extra SSD. Never had any issues.

@magicalwonders
I am not sure why you want to change to GPT. According to your screenshot, your pc is capable to run as MBR as well as UEFI, UEFI is usually only needed when large Boot drives are in play ( >2TB). I know UEFI has a larger address range regarding hard drives but in your case with a 120GB, IMHO that is not needed. If I am wrong, please let me know as I have not much experience with UEFI (only have one PC with that)
 
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Hi magicalwonders,

my suggestion would be to back-up all files to an external medium (pic; docs etc) and use something like GParted* (free partitioning tool) to completely wipe the HDD and then reset BIOS to default which will clear any changes you made, then install W10 on a blank HDD and it should default to NTFS format!.

*You will need to create a bootable USB stick or DVD and boot from it!.

https://gparted.org/download.php

See also:

https://gparted.org/documentation.php

I hope it helps. :):):)
 
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@Saltgrass I've been running Windows 10 and my programs on the SSD for about two years now. I have 40GB spare capacity, so should be ok for a while. At the time I purchased, it was a question of cost and what I could get away with. I will upgrade though when I start to get low on space. I guess the cost of SSD has probably come down a bit in two years.

@Grizzly There are some other advantages to GPT, other than number of partitions that can be created. According to some tests I've seen, I'll get a faster boot up time. Not much, but it all helps. There are some security advantages as well. At some point I will do a fresh install of Windows. So I'm going to convert the disk now and see how things run. I can always restore my drive to MBR if it's a disaster!

@Wolfie Thanks for the link. That could prove a useful tool at some point! :)
 
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Hey guys,

A quick update. I took the plunge and used mbr2gpt. It worked well and converted successfully. It has actually shaved about 15 seconds off my boot time! Way more than I was expecting.

My disk management is now as in the pic below. From what I understand of GPT, I don't need the System reserved partition? It should be safe to delete, yes?

 
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@Wolfie The conversion to GPT seems to have changed things. The System Reserved partition has now been assigned a drive letter. In my case F: Only two files in there. One refers to Macrium Reflect, the other two are empty. 0 KB

I believe the boot up sequence now only makes use of the newly created EFI partition.
 
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Here's a clearer screenshot of my Disk management -



The new partition of 100MB created by the conversion is expected. I've changed the drive letter of the System Reserved partition as I want to use F: for an external drive.

Microsoft docs have this to say about the EFI partition -

If the existing MBR system partition cannot be reused, a new ESP is created by shrinking the OS partition. This new partition has a size of 100MB (or 260MB for 4K sector size disks) and is formatted FAT32.

The new partition is FAT32, so I guess everything is as it should be. Regarding the System Reserved partition, it says -

If the existing MBR system partition is not reused for the ESP, it might be assigned a drive letter. If you do not wish to use this small partition, you must manually hide the drive letter.

A drive letter has been assigned, so I'm confident that the System Reserved partition is no longer being used in the boot up process. Well I don't wish to use the partition, but they haven't made it very clear when it comes to deleting it. As it's not being used, I'm struggling to see what the point of it is.

I think to be on the safe side though, I'll seek confirmation on the Microsoft forum.
 
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Here is a pretty good explanation of how and why UEFI/GPT. Since we're using Macrium Reflect I don't think the RE-Partition is really needed as its used for Reset Recovery. Which if we have good MR SSD/Disk Images would not be used anyway?
My SSD 1 first partition is a recovery partition properties say its an OEM Recover partition. Now this has Changed since I have upgraded to 1809 before that I had 3 Recover partitions as when 1709 installed it created its own RE partition, then 1803 also created its own RE partition so this is new to me that 1809 actually integrated in my original OEM RE partition and deleted all the other RE partitions. I just noticed this since reading this thread. I have never used this partition since I use MR but I keep it for the time I buy a new notebook and want to put this notebook back into the original as-shipped condition to sell or hand down to a family member.

https://docs.microsoft.com/en-us/windows-hardware/manufacture/desktop/configure-uefigpt-based-hard-drive-partitions#recommendedpartitionconfigurations
 
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The EFI partition is now your System partition and does contain the boot files. You recovery configuration, however, may still use the System Reserved Partition.

You do not want the drive letter on the small partition since you will start getting a disk full type message.

If you want to check your recovery options, open an admin command prompt and type the following command.

reagentc /info

You can copy and paste the results. It should show where Windows will look for your Repair Tools.
 
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@Saltgrass Thanks for the info. I ran into a bit of a disaster. I accidentally deleted a scheduled task for backing up the registry. So I restored an image, which reverted the drive to MBR, then after updating the bios, I was able to start Windows.

I then repeated the conversion from MBR to GPT but then found I couldn't boot into Windows! My Windows repair disk couldn't fix the issue, and restoring a system image didn't work either! . Eventually I managed to restore an image from September, so I'm back in business. I was going to do a fresh install at this stage, but of course Windows complains that the drive is not GPT. :(

I've decided to carry out a fresh install in a few days, so will update the drive to GPT at that time. :)
 
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I was going to do a fresh install at this stage, but of course Windows complains that the drive is not GPT. :(
OK, we discussed this already. When you do a clean install, during the part where it asks you where to install Windows, just delete all the partitions on that drive...

Be careful and do not delete partitions on other drives....
 
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OK, we discussed this already. When you do a clean install, during the part where it asks you where to install Windows, just delete all the partitions on that drive...

Be careful and do not delete partitions on other drives....
Will do. I'll have to convert to GPT first though. The windows install disk wouldn't let me do anything whilst the drive is MBR. The install disk has a format function as well. Once I delete the partitions, should I format it. or does Windows do that as part of its install? I notice there is a "format" button available, as well as "delete".
 
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I'll have to convert to GPT first though.
No,no,no, if the install media is booted as UEFI then it will not have a problem...

If you wanted to clean the drive with Diskpart first, that would work also. Then it is not initialized and Windows can't complain, no matter what.

I always suggest removing other drives in the system, just to cut down of possible user mistakes.
 
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@Saltgrass I'm pretty sure I did boot install disk with bios set to UEFI but Windows complained about disk needing to be GPT. :confused: Maybe I got it wrong though. I was switching the bios back and forth quite a bit, trying to get back into Windows!

What I don't understand is, if Microsoft only want Windows 10 installing on GPT, why did it let me put it on as MBR in the first place! It doesn't make any sense. :(
 

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