Accidentally formated external hard drive (2TB) with bootable UBUNTU iso (v.17.04, 64bit,1,5GB), how can I recover my data? [duplicate]

Question

So there's the problem: I wanted to create a bootable USB from an ISO image BUT I accidentally I did that one on my external hard disks instead of the usb. Now that drive is 2TB and it was full of picture, files etc. I would like to recover as much as possible from that. Since I'm pretty a n00b with Ubuntu I'm trying to figure out how to use Testdisk (which I've heard it's a very good tool for data recovery).
Questions:

1. is it not possible just to unmount the iso in order to get again access to the other files? Does the mounting "formats" in some ways the rest of the drive?
2. Testdisk asked me to specify the partition table type, what is and what I should answer?
3. There are other possible ways to recover the data? I mean, nothing was "really" formatted and also the iso is not big enough to mess everything up.

Sorry if those questions are out of topic of not so detailed, and thanks for any possible answer.

Answer 1

You probably don't want test disk in the first instance, you want photorec which is part of the test disk suite. (Photorec is easy to use for a start)

Photorec will ignore the disk format and look for what it can recover regardless of filesystem. Unfortunately this means it will loose filenames, files which have been fragmented and files without a recognisable sig - and it will find old deleted versions of files you want).

Testdisk is more advanced and serves a different purpose. Before you use it you should clone the disk so if you stuff up you can try again. Testdisk is designed to handle lost stuffed up partitions with in-tact filesystems. Sometimes, depending on the Filesystem you can get lucky and partially recover from a backup file table structure. This is quite complex and filesystem dependant.

If the disk was used in Windows it is most likely formatted with a version of the FAT filesystem or NTFS. There are different numbers associated with these, but we can't advise without knowing more. That said, it's probably academic in light of your skill level. If the disk was a typical external drive with 1 large partition, writing Ubuntu would have overwritten the first part of the disk - the part which holds the file allocation table or equivalent.