I'm a paranoid with backups, but Murphy's law is always around the corner... so last evening my main storage (a raid1 nas) after a power failure became corrupt (windows prompts: "The drive is not formatted, do you want to format it now?") and I realized that some days ago I've sold my external usb drive, as my new usb3 drive was incoming by mail.
After testing many applications, I've found what has saved me:
TestDisk and PhotoRec
They are both free and often updated, TestDisk tries to recover the original file and folder structure, reconstructing the partition table, PhotoRec analyzes the raw data, recognizing know file patters (including .arw, .dng, ect...), but loosing the original name and location.
You should first try TestDisk, running a whole disk surface scan, only in case it fails you can run PhotoRec.