Strange partition alignment after WRITE test

Hi

I did WRITE test by HDSentinel for 8TB HDD. Test destroyed existing partition and now I am trying to create a new partition, but hard drive looks strange in many partition tools. No bad or weak sectors.

Aomei shows one whole stretch of unallocated space and when I tried to create new partition, Aomei allows only 2TB partition to be created, leaving the rest of hard drive as unallocated. It doesn't allow to increase partition size.

I tried EaseUS Partition Master Personal - almost the same results, but EaseUS shows MBR partition as well, but can not do anything else, but to create only 2TB partition (out of 8TB space).

Win 8.1 Disk Management shows 2 RAW partitions, one 2TB and the other 6TB (it is not exactly 6TB, but I am rounding up for the simplicity of conversation).

What is going on, how to make hard drive come back to normal state with only one partition?

Right now I decided to wipe HDD with Aomei 1 pass, will take time. Hopefully it will overwrite/wipe MBR as well, as I am trying to return disk to pre-sale condition and allocate as GPT with only one partition.

Any suggestions appreciated (remember Aomei wipe is in progress, so I can not do much with the drive right now, just gathering info for next steps).

Thanks in advance.
 


Thanks for suggestion, but it is not what I asked.

Final result will be GPT, but that is an easy part.

Right now I can only create 2TB partition on 8TB drive in perfect condition mechanically.
And I need only one 8TB partition.
Something got messed up.
This is the problem.

Edit. I am doing Aomei wipe right now to attempt to erase remnants of MBR mess I have.
Worst come to worst, I would have to repeat WRITE test, but it takes 14 hours in my case...

Edit 2.
If I do only partial WRITE test as sequential, starting in the beginning of the disk, would it first overwrite MBR partition? In this case I can stop the test earlier and save at least 10 hours of my time?
 
Let me rephrase my main question.

I need to erase my hard drive (data hard drive, not system) and start all over, erase remnants of MBR structure, make a disk like it just came from the store.

I prefer Windows environment, so I prefer not to use DBAN if possible.