Accidentally written a bootable image to an external HD

[Tricerawhoops]

I was trying to get a 65MB bootable image (Nook Manager, for rooting my Nook ebook reader) to write to an SD card in Win32 Disk Imager. Somehow it must have selected my external HD and written the image to that instead. Because I was having problems with writing to the SD card, I opened up the disk management control panel to delete the partition from what I thought was the SD card. Only after I'd done that did I see that the 1TB external HD was showing as ~930GB of unallocated space.

I've run EaseUS Partition Master and it didn't appear to find anything (assuming I ran it properly). I first ran MiniTool Partition Recovery. Even on a 'fast' scan it ran very slowly (it took about half an hour to reach 3% progress). It found a FAT16 partition for Nook Manager with Starting LBA 32 and Ending LBA 131071. I cancelled the scan at around 6% after further reading suggested it might not find a partially-overwritten partition.

I then tried Test Disk, on a 'quick' partition analysis running overnight. It looks like it had the same limitation as Partition Master and was only able to identify the NOOKMANAGER partition and nothing else.

Am I right in assuming that if a new partition, however small, is written to the external HD (which was a single partition), then the old partition is completely destroyed? However, I'm also assuming that there's a large chunk of my data (roughly 400GB worth) that is still there - it's just inaccessible. Is that correct?
Since I realised my mistake, I haven't done anything to write to the disk or configure it.
I'm wondering what my options are in these circumstances. Is there particular software that will be able to extract the remaining inaccessible data or can restore the remainder of the old partition?

[pclab]

You can try with R-Studio or Get Data Back for instance.
You should get some files, but you can end up with allot of files corrupted.
I had a case a few days very similar and not a very good luck I got....

[dick]

Hi! A raw recovery would probably get back most of your files but without the folder and file name structure.

Alternatively presuming your partition type was either ntfs or fat I would try using Dmde and see what it can find. Good luck!

[fzabkar]

I would first confirm the extent of the damage. To this end I would use a disc editor (eg DMDE freeware) to copy the first 131072 sectors of your corrupted HDD to a file. Then compare this file against your Nook Manager image. If the files are identical, then this would confirm that LBAs 0 to 131071 were overwritten. If there is a difference, then take note of the sector at which it occurs, say sector N.

My next step would be to clone the drive, sector by sector, and write zeros to the first 131072 or N sectors of the clone, whichever is applicable. This would prevent your data recovery software being confused by the contaminated data.

If your drive was partitioned with an NTFS file system, then DMDE should be able to locate a backup boot sector at the end of the drive. Can you show us DMDE's partitions window?