I accidentally used win32diskimager and wrote an image onto my 1tb external hard drive. I panicked, aborted the win32diskimager process and found out my ext hdd couldn't be formatted.

Next, I wrote a small 4mb image using win32diskimager and after which I could formate the ext-hdd. Since I've really only written a small amount of data onto my ext-hdd (I would guess no more than 100-500mb), I presume that the majority of files are still recoverable.

Are there any advice you guys can give?