Ask HN: Good books about filesystems?

Aproaching the new Mac OS, i´ve heard a lot of people complain about it´s obsolete filesystem as of now, and how Apple should change to a new one soon.

Thing is, i don´t quite get why one is better than the other, or what is a filesystem exactly, besides the basics. Is there any good book or blogpost with a modern approach as to what they are, and what are the best ones, the basics of how they are programmed, etc?