du only counts the file contend and a part of the meta data (not counting e.g.
the "inode" - see: /usr/include/sys/fs/ufs_inode.h)
Right, but the timestamps, owner, and mode only take up a handful of
bytes, which cpio also stores.
The cpio archive format -Hcrc never has become a standard and the POSIX cpio
format
has been declared obsolete 5 years ago because it it not extensible.
Less useful formats may have less overhead but this is an inferior argument
if you have to decide for a portable and extensible format. The POSIX cpio
format is e.g. limited to 8 GB files and the SVr4 crc format is limiet to even
less.
If you like to have an archive format that completely fits your actual needs,
you will end up wit > 100 incompatible archive formats.
If you compress the result, the remaining difference is less than 1%.
I'd say archiving my Maildir is a rather real world use, so this is
somewhat relevant. I did notice though, that once compressed, the
difference in size is greatly diminished.
See above.
Jörg