this is a behavior that dates back to Unix System 5 - the ability to write archives larger that can be read -- the mythical "Write Only Memory" problem.

This is my question:  I assume that the problem cannot be easily fixed or someone would have fixed it, but why does cpio OUT not generate an error when it writes the first byte that cannot be read back?   It seems inconsistent to me - either the program can read back all the bytes it writes, or it produces an error when asked to write a byte beyond it's own read capacity.

Maybe it simply can't be done - except TAR can manage to read back any archive it creates.  Why can't CPIO?