Ilyet az mdadm is tud, a create-nek add meg: --assume-clean
„Some people have noticed the --assume-clean option in mdadm and speculated that this can be used to skip the initial resync. Which it does. But this is a bad idea in some cases - and a *very* bad idea in others.”
https://raid.wiki.kernel.org/index.php/Initial_Array_Creation
(Egyébként miért zavar, hogy a _háttérben_ megy a resync?)