Size of installations ?

I was wondering how much storage people are putting behind their  
storage heads ?

I can see that a 3170 nominally goes up to 840TB or 420 per head but  
do people actually put that much storage on a single unit ?

I can see that the V series supports SVC, how common is this  
configuration ?

We need to be aiming for about a half Petabyte per rack, I can see how  
I could do this with a DDN S2A9900 behind an SVC, I would be  
interested to hear peoples opinion.