AAAAHHH but i did take that into account (:

so you could lose up to 8 drives (2 per individual raid 6) and still be able to restore your data on each of the 4 raid 6 pieces. BUT you're also allowed to lose two of the individual raid 6's so you could tack another 4 drives onto the total taking out two of your raid 6's. Grand Total by my strange calculations = 12 down'd drives

meaning that those extra four drives would all be contained in just two of the 4 raid 6 pieces. so two sets of four drives completely toast and then two out of each of the other two sets totals 12 drives toast.

still. i'd be absolutely amazed to find any self respecting IT professional who fried 12 drives at once.

i still stand by my 12 drives given a perfectly frying world.