MBR to GPT utility

Windows now has a utility for converting an MBR disk
with a limited number of partitions used on it, into
GPT. (For an OS drive, that will probably mean
switching to BIOS UEFI boot, but not necessarily
UEFI+SecureBoot. Maybe the validation utility checks
for BIOS UEFI support too, but I can't be sure of that, so
be careful about what you wish for.)

For your first conversion, I recommend a full backup,
as there isn't likely to be a gpt2mbr utility also
on the drive, to undo the change.

The conversion is intended for operation from WinPE
(emergency boot CD, or booting the installer DVD to
Command Prompt). That way, C: is unmounted and no busy
file system can prevent the conversion. But the validation
procedure can be run from the comfort of your regular
OS, so no reason for immediate panic.

http://www.thewindowsclub.com/mbr2gpt-tool-windows-10

I'm hours and hours away from testing that, as I
have to clean off a large disk first, and that's
going to take a while.

The utility will run from within Windows, when you
ask the utility whether a particular disk can be converted.
The disks should be numbered in the same order as you
would find them in Disk Management.

mbr2gpt.exe /validate /allowFullOS /disk:0

It will apparently create an EFI partition of some sort,
and maybe it attempts to do that, just before the actual
step to make a GPT disk. That might be why it has a three
partition limit, before you start. Just a guess, subject
to validation. I also don't know if it's clever enough
to deal with Extended/Logical setups or not. That would
be even more messy.

My dual boot Win10/Win10 install, validation fails,
because there are too many partitions. The disk has
System Reserved, Recovery, Win10a, Win10b, which is
too many. The Win10 I have running in a VM has only
two partitions, and it is passing validation right now.

As for what OSes it will accept, it's supposed to
accept Win10 OS drives (because it knows how to modify
the BCD). It should really be able to handle anything
from Vista to Win10, because the target OS has the necessary
utilities to regenerate the BCD. But you know Microsoft.
They could make a Shrink capability that stops at 50%
of the partition, so it was easy to limit the OS support
on this one for them :-)

Still, if you're bored, it's worth a shot. It might
take me a while before I can give first hand results.
I actually need to do this right now (make a boot drive
with a large C, but first I have to free up a 4TB drive
to do it, then clone over from my regular boot drive,
before I can test. I will then switch the new drive
to GPT, just before expanding the C: partition past
the 2TB point.

Paul

"Paul" wrote in message
news
Windows now has a utility for converting an MBR disk
with a limited number of partitions used on it, into
GPT. (For an OS drive, that will probably mean
switching to BIOS UEFI boot, but not necessarily
UEFI+SecureBoot. Maybe the validation utility checks
for BIOS UEFI support too, but I can't be sure of that, so
be careful about what you wish for.)

For your first conversion, I recommend a full backup,
as there isn't likely to be a gpt2mbr utility also
on the drive, to undo the change.

The conversion is intended for operation from WinPE
(emergency boot CD, or booting the installer DVD to
Command Prompt). That way, C: is unmounted and no busy
file system can prevent the conversion. But the validation
procedure can be run from the comfort of your regular
OS, so no reason for immediate panic.

http://www.thewindowsclub.com/mbr2gpt-tool-windows-10

I'm hours and hours away from testing that, as I
have to clean off a large disk first, and that's
going to take a while.

The utility will run from within Windows, when you
ask the utility whether a particular disk can be converted.
The disks should be numbered in the same order as you
would find them in Disk Management.

mbr2gpt.exe /validate /allowFullOS /disk:0

It will apparently create an EFI partition of some sort,
and maybe it attempts to do that, just before the actual
step to make a GPT disk. That might be why it has a three
partition limit, before you start. Just a guess, subject
to validation. I also don't know if it's clever enough
to deal with Extended/Logical setups or not. That would
be even more messy.

My dual boot Win10/Win10 install, validation fails,
because there are too many partitions. The disk has
System Reserved, Recovery, Win10a, Win10b, which is
too many. The Win10 I have running in a VM has only
two partitions, and it is passing validation right now.

As for what OSes it will accept, it's supposed to
accept Win10 OS drives (because it knows how to modify
the BCD). It should really be able to handle anything
from Vista to Win10, because the target OS has the necessary
utilities to regenerate the BCD. But you know Microsoft.
They could make a Shrink capability that stops at 50%
of the partition, so it was easy to limit the OS support
on this one for them :-)

Still, if you're bored, it's worth a shot. It might
take me a while before I can give first hand results.
I actually need to do this right now (make a boot drive
with a large C, but first I have to free up a 4TB drive
to do it, then clone over from my regular boot drive,
before I can test. I will then switch the new drive
to GPT, just before expanding the C: partition past
the 2TB point.

Paul

Very informative. Thanks!

My C: drive is GPT (came with this Win10 PC), but my D: drive is MBR (the
one I use for misc. files, movies, program installers, etc.). Is there any
advantage to converting it to GPT also, or should I just leave well enough
alone?

--

SC Tom

SC Tom wrote:


"Paul" wrote in message
news
Windows now has a utility for converting an MBR disk
with a limited number of partitions used on it, into
GPT. (For an OS drive, that will probably mean
switching to BIOS UEFI boot, but not necessarily
UEFI+SecureBoot. Maybe the validation utility checks
for BIOS UEFI support too, but I can't be sure of that, so
be careful about what you wish for.)

For your first conversion, I recommend a full backup,
as there isn't likely to be a gpt2mbr utility also
on the drive, to undo the change.

The conversion is intended for operation from WinPE
(emergency boot CD, or booting the installer DVD to
Command Prompt). That way, C: is unmounted and no busy
file system can prevent the conversion. But the validation
procedure can be run from the comfort of your regular
OS, so no reason for immediate panic.

http://www.thewindowsclub.com/mbr2gpt-tool-windows-10

I'm hours and hours away from testing that, as I
have to clean off a large disk first, and that's
going to take a while.

The utility will run from within Windows, when you
ask the utility whether a particular disk can be converted.
The disks should be numbered in the same order as you
would find them in Disk Management.

mbr2gpt.exe /validate /allowFullOS /disk:0

It will apparently create an EFI partition of some sort,
and maybe it attempts to do that, just before the actual
step to make a GPT disk. That might be why it has a three
partition limit, before you start. Just a guess, subject
to validation. I also don't know if it's clever enough
to deal with Extended/Logical setups or not. That would
be even more messy.

My dual boot Win10/Win10 install, validation fails,
because there are too many partitions. The disk has
System Reserved, Recovery, Win10a, Win10b, which is
too many. The Win10 I have running in a VM has only
two partitions, and it is passing validation right now.

As for what OSes it will accept, it's supposed to
accept Win10 OS drives (because it knows how to modify
the BCD). It should really be able to handle anything
from Vista to Win10, because the target OS has the necessary
utilities to regenerate the BCD. But you know Microsoft.
They could make a Shrink capability that stops at 50%
of the partition, so it was easy to limit the OS support
on this one for them :-)

Still, if you're bored, it's worth a shot. It might
take me a while before I can give first hand results.
I actually need to do this right now (make a boot drive
with a large C, but first I have to free up a 4TB drive
to do it, then clone over from my regular boot drive,
before I can test. I will then switch the new drive
to GPT, just before expanding the C: partition past
the 2TB point.

Paul

Very informative. Thanks!

My C: drive is GPT (came with this Win10 PC), but my D: drive is MBR
(the one I use for misc. files, movies, program installers, etc.). Is
there any advantage to converting it to GPT also, or should I just leave
well enough alone?


GPT is a mechanism for handling 2.2TB capacity drives.

GPT is good, if you have an excessively large number
of partitions. But the usage of GPT also encourages
the addition of more partitions. Which is why a Dell or HP
computer today, with a 1TB boot drive in it, might be
partitioned GPT with five or six partitions. Many of
the partitions, there's no documentation as to what
they're for. (We know at least one has a copy of the
factory restore, but is that a 4GB thing or a 12GB thing?
That's what isn't documented, as to which partitions
are really valuable, and which ones could be turfed.)

If you use GPT, you might find you end up using a
slightly different set of third party applications.
If you're going to do a boot drive with that, "expect
to learn stuff" :-) You'll need a UEFI BIOS to boot from
GPT. You'll need an OS with GPT support. If you put
WinXP on a GPT disk... well, that would be an interesting
experiment.

In a way, it's like using RAID. Then, the RAID array breaks
and you need to do data recovery... And you discover
that data recovery applications for RAID cost $$$. Then
you realize what a mistake RAID was. And why you can't
really run RAID without a backup, as a backup costs $,
while data recovery software costs $$$. Backups are
cheaper. Simple configs are cheaper.

But if you (easily) want to use all the capacity
on that new 10TB data drive, then GPT is an answer
for that. That's what I'm doing for my large
backup drives. Currently I own nothing larger
than 4TB for backup. It takes a long time to
transfer the files off one, and managing larger
drives just wouldn't be practical.

As an example, yesterday I'm doing a procedure that
takes 13 hours. The procedure is data safe. I get to
the 12 hour 40 minute point... and the power goes off!
And I can't rely on my UPS (no countdown timer) to tell
me whether I have enough capacity to finish. So I have
to dump the run and start over, when the power comes
back. This is one reason I'm not all that interested
in owning a drive that will increase some run to
30 hours or something. I would have to buy a
Power Wall from Tesla :-)

Paul

In article , lid says...

SC Tom wrote:


"Paul" wrote in message
news
Windows now has a utility for converting an MBR disk
with a limited number of partitions used on it, into
GPT. (For an OS drive, that will probably mean
switching to BIOS UEFI boot, but not necessarily
UEFI+SecureBoot. Maybe the validation utility checks
for BIOS UEFI support too, but I can't be sure of that, so
be careful about what you wish for.)

For your first conversion, I recommend a full backup,
as there isn't likely to be a gpt2mbr utility also
on the drive, to undo the change.

The conversion is intended for operation from WinPE
(emergency boot CD, or booting the installer DVD to
Command Prompt). That way, C: is unmounted and no busy
file system can prevent the conversion. But the validation
procedure can be run from the comfort of your regular
OS, so no reason for immediate panic.

http://www.thewindowsclub.com/mbr2gpt-tool-windows-10

I'm hours and hours away from testing that, as I
have to clean off a large disk first, and that's
going to take a while.

The utility will run from within Windows, when you
ask the utility whether a particular disk can be converted.
The disks should be numbered in the same order as you
would find them in Disk Management.

mbr2gpt.exe /validate /allowFullOS /disk:0

It will apparently create an EFI partition of some sort,
and maybe it attempts to do that, just before the actual
step to make a GPT disk. That might be why it has a three
partition limit, before you start. Just a guess, subject
to validation. I also don't know if it's clever enough
to deal with Extended/Logical setups or not. That would
be even more messy.

My dual boot Win10/Win10 install, validation fails,
because there are too many partitions. The disk has
System Reserved, Recovery, Win10a, Win10b, which is
too many. The Win10 I have running in a VM has only

Yea, I also find the increasingly larger hard disks are becoming
increasingly also more of a pain when wanting to make a copy etc.

Paul wrote:
SC Tom wrote:


"Paul" wrote in message
news
Windows now has a utility for converting an MBR disk
with a limited number of partitions used on it, into
GPT. (For an OS drive, that will probably mean
switching to BIOS UEFI boot, but not necessarily
UEFI+SecureBoot. Maybe the validation utility checks
for BIOS UEFI support too, but I can't be sure of that, so
be careful about what you wish for.)

For your first conversion, I recommend a full backup,
as there isn't likely to be a gpt2mbr utility also
on the drive, to undo the change.

The conversion is intended for operation from WinPE
(emergency boot CD, or booting the installer DVD to
Command Prompt). That way, C: is unmounted and no busy
file system can prevent the conversion. But the validation
procedure can be run from the comfort of your regular
OS, so no reason for immediate panic.

http://www.thewindowsclub.com/mbr2gpt-tool-windows-10

I'm hours and hours away from testing that, as I
have to clean off a large disk first, and that's
going to take a while.

The utility will run from within Windows, when you
ask the utility whether a particular disk can be converted.
The disks should be numbered in the same order as you
would find them in Disk Management.

mbr2gpt.exe /validate /allowFullOS /disk:0

It will apparently create an EFI partition of some sort,
and maybe it attempts to do that, just before the actual
step to make a GPT disk. That might be why it has a three
partition limit, before you start. Just a guess, subject
to validation. I also don't know if it's clever enough
to deal with Extended/Logical setups or not. That would
be even more messy.

My dual boot Win10/Win10 install, validation fails,
because there are too many partitions. The disk has
System Reserved, Recovery, Win10a, Win10b, which is
too many. The Win10 I have running in a VM has only
two partitions, and it is passing validation right now.

As for what OSes it will accept, it's supposed to
accept Win10 OS drives (because it knows how to modify
the BCD). It should really be able to handle anything
from Vista to Win10, because the target OS has the necessary
utilities to regenerate the BCD. But you know Microsoft.
They could make a Shrink capability that stops at 50%
of the partition, so it was easy to limit the OS support
on this one for them :-)

Still, if you're bored, it's worth a shot. It might
take me a while before I can give first hand results.
I actually need to do this right now (make a boot drive
with a large C, but first I have to free up a 4TB drive
to do it, then clone over from my regular boot drive,
before I can test. I will then switch the new drive
to GPT, just before expanding the C: partition past
the 2TB point.

Paul

Very informative. Thanks!

My C: drive is GPT (came with this Win10 PC), but my D: drive is MBR
(the one I use for misc. files, movies, program installers, etc.). Is
there any advantage to converting it to GPT also, or should I just
leave well enough alone?


GPT is a mechanism for handling 2.2TB capacity drives.

Well, the GPT2MBR test is done.

It took me twice as long as expected to clear off the
4TB disk. But then, I was able to clone my Insider setup
to the 4TB drive.

+-----+-----------------------+--------+----------------+--------+- -
| MBR | System Reserved 350MB | Win10B | Recovery 450MB | Win10A |
+-----+-----------------------+--------+----------------+--------+- -

Well, the validate command didn't like the setup, because four
partitions are used, instead of a max of three. I tried deleting
the Recovery, after checking "reagentc" command to verify it
was disabled. Recovery actually had a WinRE in it, but because
this was a test clone, I could trash it without worrying. I
was more worried about damaging the BCD and not being able
to boot.

OK, so now I'm down to three partitions. I run the "validate"
option and it says my setup is ready to go. Boot the Windows 7
backup emergency boot CD, run mbr2gpt from there, and it
validates OK, but when you actually run "convert", it bails
saying it cannot find the OS partition.

I tried various repair techniques, and the situation did not
improve. It doesn't seem to handle a dual boot all that well,
by the looks of it.

Next, I deleted Win10B, leaving just SR and Win10B. "Validate"
at OS level liked that. And "convert" from WinPE was willing to
convert it. It ended up looking like this.

+-----+-----------------------+--------+----------------+--------+- -
| MBR | EFI Partition 350MB | | | Win10A |
+-----+-----------------------+--------+----------------+--------+- -

I was then allowed to resize C: on the end, to fill the
disk, and C: is now 3.6TB in size. It boots OK, using UEFI
boot. The BIOS boot menu recognizes it's a UEFI disk now and
labels the popup boot accordingly, and there's no longer
a legacy boot option for the disk showing.

The Disk Management diagram, I don't think it shows the 128MB
GPT partition table.

The application I'm running, still isn't 100% happy.
"Wish I had source" :-)

Paul