NASA Pleiades Supercomputer
With 195 thousand cores, it can hit 2.9 petaflop/s. With 65 miles of cable, it's the largest InfiniBand network in the world.
Pleiades also has the capability to have capability expansions and hot swaps without an interruption of operations.
After seeing the photo above, I realized that I felt compelled to take a similar pose to the one I used inside the Cray X1 at Oak Ridge National Labs... (see below)