cdb.vff is a "virtual FAT filesystem" that contains, among other things, the contents of the Wii Message Board, including emails and playtime records.
|0||4||'VFF' and 0x20||4-byte magic|
|4||2||feff||Byte order mark (in this case, big endian)|
|6||2||0100||? (2's complement of previous field ?)|
|8||4||01400000||Total file size|
|12||2||0020||Offset to start of first FAT|
There are two FATs, one located at offset 0x20, the other at 0x14020. They should generally be identical.
The root directory begins at 0x28020; see http://en.wikipedia.org/wiki/File_Allocation_Table#Directory_table for the format.
Clusters seem to be 0x1020 bytes each (!?!)