Unformatted external hard disk drive data recovery

Have you ever meet external hard disk drive unformat error? CHKDSK is not available for RAW external hard disk when you want to recover data? We can not use the external hard drive if it is in not formatted trouble. As a result, we can not read files or folders saved on the external hard disk drive at the previous time. What if those original contents on the external hard disk drive are important or useful? Actually, we can perform data recovery on the unformatted external hard disk drive.