I understand you are talking about "
smartmontools"? It deals with the SMART values that are related to the health of a hard drive. Space has nothing to do with a hard drive. A hard drive is just a device that holds a bunch of bytes. It may or may not be partitioned (with various partition formats) into a bunch of partitions, each of which which may or may not be partitioned further with logical partitions, each of which may or may not be formatted in one of dozens of filesystems that the OS understands. And the concept of "space" only makes sense to the particular filesystem, since it is the filesystem that keeps track of what is "used" and what is "free". So the best way to see how full something is is to mount it, and then run "df", or something equivalent.