How to safely remove rest of GTP?

[Warren Block]

On Tue, 31 Jan 2017, Andrey V. Elsukov wrote:

> On 31.01.2017 18:43, Rodney W. Grimes wrote:
>> ... much deleted ...
>>> 
>>>> It is impossible to have a corrupted GPT and some
>>>> other type of partition table in the same time.
>> 
>> I believe that statement is in error.
>> dd if=/boot/boot0 of=/dev/ada0
>> Would not that lead to this very situation if done
>> to a GPT parted disk drive?
>
> No, it will not lead to this situation.
> /boot/boot0 is similar to /boot/mbr in the example, and with /dev/ada0 all 
> will behaves like with /dev/md0.
>
>>> Maybe when only using FreeBSD and gpart, but I'm pretty sure I've seen
>>> forum users who have tried some crappy other formatting tool and have
>>> overwritten the primary GPT with a valid MBR and left the secondary GPT
>>> untouched.  This only becomes obvious when they bring the disk back to a
>>> FreeBSD system.
>> 
>> As almost all MBR tools are un aware of GPT so well not do anything to
>> destroy the secondary GPT, so this is infact very likely to occur.
>
> Please, give me some working example, when or where you have a problem, and 
> not some theoretical, based on previous negative experience or memories.

I just encountered something similar with a Windows 7 install on a disk 
that previously had a FreeBSD GPT layout.

Clonezilla reported a conflicting GPT/MBR layout on the disk.  In gpart, 
it showed a valid GPT (not corrupt) with no partitions.  After all the 
cursing, I ran 'sudo sgdisk -z /dev/sda' as instructed by Clonezilla.

It was only after that I realized I should have saved at least the 
partition tables.