A free form string indicating the algorithm or tool used to compress the file system. If it is not possible or not desired ...

A free form string indicating the algorithm or tool used to compress the file system. If it is not possible or not desired to describe the compression scheme (perhaps because it is not known), recommend using the following words: \"Unknown\" to represent that it is not known whether the file system is compressed or not, \"Compressed\" to represent that the file system is compressed but either its compression scheme is not known or not disclosed, and \"Not Compressed\" to represent that the file system is not compressed.