Copiado del man de e2fsck:
Instead of using the normal superblock, use an alternative
superblock specified by superblock. This option is normally
used when the primary superblock has been corrupted. The loca-
tion of the backup superblock is dependent on the filesystem's
blocksize. For filesystems with 1k blocksizes, a backup
superblock can be found at block 8193; for filesystems with 2k
blocksizes, at block 16384; and for 4k blocksizes, at block
32768.
Significa que los superbloques backup se encuentran en el bloque 8193 si tienes el tamaño del bloque a 1k, en el 16384 si lo tienes de 2k y en el 32768 si lo tienes de 4k
