Clashes are technically possible, but in reality they are incredibly unlikely.
From http://search-hadoop.com/m/VYVra2krg5t1:
The probability of a given random 16-byte string appearing in a petabyte of (uniformly distributed) data is about 10^-23. It's more likely that your data center is wiped out by a meteorite (http://preshing.com/20110504/hash-collision-probabilities).