In normal precreate (not the first one which will try deleting orphans) the last_id on OST is always trustable, because it's maintained in memory, and rarely OSP may try to precreate with a stale last_id (even more than OST_MAX_PRECREATE), it should be OSP that messes up the last created FID, always reply OSP with current last_id, so that OST won't become unusable.