I was installing OpenBSD on a hard disk with about a dozen partitions: NTFS, FAT, EXT3, EXT4 and LUKS. I made a mistake and told OpenBSD to use the whole disk instead of one partition. I realized my mistake some 4 or 5 seconds later, then I pressed Ctrl+c and killed the process. Now I have a blank HDD with a very large partition, a very small partition and no more Grub.

I have backups, but they are a few days old and there are things I would like to recover if possible. Do you think that's possible? Is there any software that will look at that disk and guess where each partition used to begin and end? I am pretty sure the most important stuff was in the last partitions, toward the bottom. The first partition was 30 GB and had Windows, totally expendable. Then there was 3 GB of FAT. Then an empty 30 GB partition for BSD... The important stuff comes after that.

You see, just finding software on Google is easy. I would like to hear from people who had some experience similar to mine and managed to solve it. You know how data loss is, I am not thinking very clear right now. I'm bummed...

Testdisk is the usual answer to this. It scans the disk looking for partition "signatures" - depends a bit on how much you overwrote. May also find older partitions as well - no real problem if you have an idea of what was on there.

Testdisk didn't solve things magically, I had to do a lot of the legwork, but it provided very useful hints. In the end, I recovered the entire disk, all partitions.

Thank you.