no disk 11 is correct.
so I shut down, removed and reseated both ends of each sata cable in the top drive cage where disk 10 lives and then powered back up. before startign the array, i set disk 10 to not installed in the main tab. then I started the array. stopped the array, and then assigned disk 10 to the new drive again and started the array back up and now it is rebuilding the data. so far so good.
and the good news is that if it was just a cable, then after the rebuild I can throw the old drive back in and expand the array.
thanks for your help with that!