Windows 10: Fun trying to convert an existing install to a vhd!

Surely I need to use a GPT vhd surely as I am UEFI based?

I was not trying to run it in Hyper-V but have it as native boot

My issue is more likely due to a glitch somewhere. I have added VHDs many times using bcdboot as a dual boot option. For some reason I cannot fathom out, it does not like one reduced in size as I described earlier. AS LX07 says it should work fine, and I agree it should.

As I said. I have solved my problem - I was just curious more than anything as to why I was having problems. In the end, if a method works, then it is not a big deal even if I took the scenic route to get to the answer.

Thanks very much for the valuable information as always.

 

First, it's irrelevant, totally irrelevant what partitioning system your host and a VHD used in native boot are using. A GPT host can add and use a MBR VHD in native boot, and an MBR host can add and use a GPT VHD.

Second, the Part Three in tutorial I linked shows how to convert a GPT VHD made with Disk2VHD to MBR. It's the easiest, simplest and fastest way to do the conversion and then be able to use the Disk2VHD vhd file in either a virtual machine or in native boot.

A GPT VHD made with Disk2VHD cannot be used as it is on virtual machine or native boot. Converting it to MBR makes things easy.

It's of course totally your own business how you do it, main thing is to succeed. I was simply telling about an option that makes it easy.

 

Kari,

I want to make sure I understand what you said. I'm staring to use Hyper-V for virtual machines.

If I create a VHD, it doesn't matter if the host is MBR and the VHD is GPT, if both are GPT, if both are MBR, or if the host is GPT but the VHD is MBR.

If all that is correct, then why does a VHD created with Disk2VHD have to be MBR to be directly bootable? *Confused

 

Because when you create a VHD with Disk2VHD from a GPT disk, it does not recognize and include the EFI System Partition in VHD it creates.

You have to remember that Disk2VHD is although still a powerful tool quite an old program. When originally coded all systems were BIOS & MBR, the program "learned" that to make a bootable VHD it needed to include the first partition on first hard disk (System Reserved partition in MBR) which contains the boot records in addition to OS and possible data partitions selected by user.

It's still using this same principle even on GPT disks. Disk2VHD includes the first partition of the first disk which it assumes contains the boot records but on GPT disk it is just a Recovery Partition (yellow highlight in screenshot below) but ignores the next partition (EFI System Partition) which on GPT disks actually is the one with boot records (red highlight):




(Click to enlarge.)

This results a totally working but not bootable VHD. The user now has two methods to make it bootable and use it on vm or native boot, either convert it to MBR or manually create the EFI system partition and boot records on it. I prefer the conversion method because it is so incredibly easy and simple.

 

Thanks for this explanation. Very clear.