conversion of GPT to MBR without data loss

I have a 4TB non-system GPT disk that is less than half full. Can I convert it to a 2TB MBR disk without loss of data?

I work in Windows XP and have been using Paragon GPT_Loader to access the GPT disk. I now wish to uninstall the GPT Loader and am prepared to lose access to half my disk provided it keeps the data it now contains.

I tried Paragon Disk Manager Pro and AOMEI Partition Assistant but they don't work, presumably because the GPT disk is > 2TB.

 

normanbg,

I assume you have a single partition on that HD. Resize it to slightly less than 2 TB and then you will be able to convert the GPT disk to a MBR disk.

 

Yes, only the one partition. I'll try resizing when I get back in to work on Sunday. Thank you.

 

Dear Brian,
I couldn't wait. So I bought a copy of Paragon Disk Manager (the Demo version does not allow one to change partition size, only to test whether it is indeed possible), decreased the partition size to 2TB and, lo and behold!, I was then able the convert the GPT disk to MBR, just as you said. I didn't actually do the conversion on my home machine (essentially the same as the one at work) because I had not prepared backups—just in case. Tomorrow I'll go the whole way on my work machine.

Brian, you saved me a lot of copying, 12TB more or less. I have two such 4TB disks on my PC at work and another two at home, and each is about 1.5TB full. That makes 6TB to back up and then the same 6TB to restore.

I am very grateful for your help. Thank you again.

 

normanbg,

That's great news. You can delete the redundant 128 MB partition if you like.

If you have a Win7/8 system and you want to use the remainder of the 4 TB HD, it's possible. The 2 TB partition you just created will still be usable in WinXP.

I use BIBM to do this. Convert your disk to GPT. Create a partition in the remaining unallocated free space. Click View MBR, select an empty MBR slot (not the GPT Reserved slot), click Insert. Select the partition you just created and click OK. Click Apply.

WinXP will see the first partition. Win7/8 will see both partitions.

 

I was wondering about that 128MB partition, thank you for returning it to me .
No, I don't have Win7/8—yet. But I'll keep your detailed instructions on file in case I do get it some day.

Norman

 

Dear Brian,
My enthusiasm appears to have been a wee bit premature.
I am at work now and repeated my steps of yesterday: resize down to half and then convert to MBR. Worked fine, as it did at home, but when I chose 'Appy' (the convert), Paragon gave me a BSOD. I rebooted and tried 'convert to MBR' again, and again 'Apply' gave a BSOD. The third time Paragon did not even offer the 'convert to MBR' option.
I reinstalled Paragon but still no 'convert to MBR' option. So I tried doing it via 'diskpart', but diskpart insisted that the disk was not empty. I formatted it (twice, actually, once in Paragon and once in XP), but diskpart still refused to convert, even when I launched it from outside Windows using a bootable rescue disk.
The disk itself appears in Windows as a 1.81TB GPT disk and seems to be functioning normally.
What do I do now?

Norman

 

Norman,

I'm not familiar with Paragon. Does it have a boot CD that you can use? The conversion is probably better done offline. Otherwise I could tell you how to do it using a BIBM trial version.

But first, try resizing the partition smaller. Make it 1.75 TB and see if Paragon works.

 

Dear Brian,
Paragon does have the option to create a bootable CD, but it will take me some time; meanwhile, I'll try decreasing the partition size. (Actually, I thought that may be the problem and did make it smaller, but clearly not enough.)
Jerusalem is GMT+02, so it will have to wait until tomorrow.
Thank you for your patience.

Norman

 

Norman,

Your partition size should have been fine. Make sure there isn't another partition above the 2 TiB mark.

 

Dear Brian,

My GPT disk has a single partition of 1.75TB, the rest of the 4TB is 'unallocated'.

I downloaded BIBM and made a boot disk. I booted, then: do not install> Work with Partition>Selected my GPT disk>Change disk type>MBR: "...could not change...".

Diskpart run in a preboot environment also did not work although, by this stage, the disk was completely empty.

Windows sees the disk as GPT with 1.74TB free space.

What am I doing wrong?

Norman

 

Norman,

In BIBM, Partition Work, what do you see in the big white rectangle labelled GPT partitions?

 

Dear dear Brian,

I booted from the BIBM CD and chose Partition Work in order to get the precise wording you asked for. I also went through the motions of Change disk type>MBR as I had done twice yesterday, so I could tell you what the error message said.

But no message appeared; instead, the conversion to MBR worked!

I don't know what I did today that I didn't do yesterday, or vise versa, but I am very happy. Even Paragon, which I was beginning to doubt, recognises the disk as MBR.

So thank you again, and again. You have been very kind, and very patient.

Norman

 

Norman,

Great news. In BIBM Partition Work, you can resize the partition up to the maximum allowed. I'd be interested to hear what maximum you are allowed.

 

Dear Brian,

The maximum allowed is 2097151MB, which is 2TB. I resized the MBR partition I had created, to this maximum and it appears to be working fine.

I then tried to resize my other GPT disk from 4TB to 1.5TB but BIBM got stuck at 88%. I waited an hour but nothing happened. So I stopped it; the data (about 0.8TB) remained intact.

Then I tried Paragon. I let it run overnight (18hr), but it too couldn't complete the job. (Paragon has no progress meter, so I don't know how far it got.) I stopped it and lost all my data. Now I have an empty 2TB MBR disk.

My 2 GPT disks at home downsized without difficulty. (All 4 disks are completely new.) I'll do the conversion later this week.

Thank you again.

Norman

 

Norman,

This might work and is worth trying. In BIBM select the unallocated free space and click Undelete. If it hasn't recovered the partition in 3 minutes call it quits. If it works it should work in a few seconds.

 

Dear Brian,

I think it's too late for that. After I stopped Paragon, I ended up with two unallocated partitions, a 1TB one and a 3TB one. I tried to do something in Paragon but couldn't. So I used Windows to create an active partition from the 1TB unallocated space, converted it to MBR using BIBM and extended it to 2TB. I then copied back onto it about 1/4 of the original material, all I had. And there it stands.

I am home now and so can't do anything until tomorrow, but I don't think anything can be done at this stage, not even a disk salvage operation.

Am I being overly pessimistic?

Norman

 

2097151 MiB is 2 TiB. That's equivalent to buying a 2.2 TB HD (digital TB).

BIBM and Windows present the numbers in MiB, GiB and TiB. (even though Windows might say MB, etc)

 

Worked just as you said. Good to know—for next time.

Yes, I know, and I was a little surprised by that.

Thank you again.

Norman