http://www.piriform.com/recuvaTry it but I think when its a RAID and depending on how its done its very difficult.
How did you have them set up?
If its a direct copy RAID 1 I think then Recuva might do it. Its very powerful and free.
I have a DNS-323 set up in RAID 1 and I think its very difficult to get the data back if both go.
Just out of interest, how did both go down? RAID is supposed to help but 2 to go down?
A tip is to use drives from different batch numbers so if the batch is faulty then you still have the other batch to fall back on.