2TB 3 partition bootable MBR to 3 partition bootable GPT 4TB drive

videobruce said:

I'll have to wait until I get the new 4TB HDD. I will experiment with setting it up as a GPT bootable.

I partly bypass the process that creates those extra partitions that waste space. I use the 'hack' that fools that install process and loads the files into only one partition instead of three. I've never had a problem with doing it that way as I have had good images of the O/S; initial with no programs and current.

Not on a GPT drive.
Normally, on a GPT drive you have:
EFI - 100M Fat32
MSR - 16M RAW
C: - Big NTFS
NTFS Data partitions

As you are converting from Legacy - MBR you probably will have
C: - Big NTFS
EFI - 100M Fat32
NTFS Data partitions

The EFI - 100M Fat32 is needed to boot as UEFI. Don't delete it or you won't boot.

- I suggest you clone the 2T MBR drive into the 4T as a MBR drive to have a backup.
- Detach all other drives from the MB leaving on only the 2T drive.
- Boot from a Win 10 installation drive and at the Windows Setup screen, press Shift+F10 simultaneously to open a command line prompt and type:
mbr2gpt /validate
It may not validate as you don't have the System partition.
if ok type:
mbr2gpt /convert
If successful, shut down, change BIOS to boot as UEFI

videobruce said:

Again, there is only one partition in my MBR drives (including the SSB & HDD drives), there is no "EFI - 100M Fat32" partition.

Why would it. An EFI System Partition is specific to GPT.

You may not have a dedicated System partition on MBR, but you do have a System partition as otherwise you would have no boot manager. Your System partition is drive C, and it's marked as active.

You cannot have a partition marked as active on a GPT disk, so you cannot have drive C as the System partition. Your System partition on GPT must be formatted FAT32, so it must be separate.

On a Legacy-MBR, BIOS transfer the boot sequence to the BIOS priority boot drive MBR that will transfer to a master boot manager on an Active partition. This master boot manager (like Linux Grub) can transfer the boot sequence to a partition (like Linux) or to another boot manager in another partition (like Windows). It is a serial chain mode.
On an UEFI-GPT, BIOS transfer the boot sequence to the BIOS priority boot manager on a Fat32 Partition and then to a OS on a partition (same drive or even to a different drive). On the FAT32 partition you may have one or many boot manager (Linux and Windows etc). It is not a serial chain mode. It is a parallel mode.

You're seeing a problem where it isn't. Let's put this way.
- Any drive bigger than 2.2T, normally formatted must be initialized as GPT to be able to use all available space. If it is initialized as MBR you will have a 2.2T partition and the remaining space will be set as unallocated and can't be used.
- GPT drive can be used as data drive in Win 7, 8, 10 (32 or 64 bits) and Win 11 (64 bits)
- GPT drive can be used as a boot able drive in Win 7, 8, 10 &11 (64 bits only )
- A GPT drive don't have a MBR so it can't be used to boot as Legacy.

In other words: to use the 4T drive it must be initialized as GPT and as a Win 7 boot able drive it must have a EFI -100M - FAT32 partition. On a 4T drive that is a little more than nothing

videobruce said:

If I initialize this new HDD, re-install W7 (x64) then, can I restore a MBR image I have from the existing install on the 2TB drive which will be removed? Will that work?

Yes you can. That is one way to convert a Legacy-MBR into a UEFI-GPT.

- Detach all other boot able drives. It is important or Win 7 can be installed on one drive and the boot manager on another
- Boot the Win 7 installation drive as UEFI and install Win 7 as UEFI-GPT
- It will create 3 partitions:
EFI - 100M Fat32
MSR - 16M RAW
C: - Big NTFS

When done, boot from the other main drive
- Delete the Win 7 partition just created. It will create a big unallocated space
- Clone the old Win 7 partition and data partition to the unallocated space created above.

Using Diskpart commands you can also initialize the new drive as GPT, create the EFI and the MSR partition, clone actual Win 7 and data partitions from the 2T drive and then load the boot manager on the EFI partition. It is faster then the previous option.
I can give you the commands.