It's not as if cp gives you anything more useful in that case. The bookkeeping that caused the problem was a hashtable of files that have been copied, necessary

It's not as if cp gives you anything more useful in that case. The bookkeeping that caused the problem was a hashtable of files that have been copied, necessary to handle hard links. Would be interesting how tar does that; if it can't do any better then the root comment and mine above are wrong.