I understand that superblocks provide high-level meta data about file systems in Linux, but how many of these structures exist for a given file system? My intuition tells me there's either one per file system, or one per file.
I recently learned that there is more than one copy of the superblock within each file system. In ext2, for example, every block group has its own superblock with identical content to the other block groups. This redundancy provides reliability in the event of a crash. So in this system, there are as many superblocks as block groups.