I totally agree.
Originally Posted by mips
One thing I was wondering about (not that it makes it any less important), aren't you miscalculating the size? 320 GB declared by vendors is actually 298GB in binary (GiB) that computer sees. Since the image size is about 278 GiB as per OP (or 283 GiB as reported by PhotoRec in the screenshot in post #13), the difference is about 20 GiB, not 40.
Although it still is a lot of data, and a lot of room for possible further problems.
To elaborate what mips said regarding point #2, your command be something like -
sudo ddrescue /dev/sda3 /media/<backup path>/image2 logfile
* /dev/sda3 is the partition you want to create image of (it should not be mounted)
* /media/<backup path>/image2 is the path and name of the 'image file' that you will be creating from the partition. All the mounted partitions (internal or an external hdd) are mounted in /media/ in Ubuntu, hence the /media/ part.
* logfile is what it says - the file that will keep log of the progress. Back it up before repeating operations, just in case..