I came here to talk about this. I deal with data management for a bunch of physics and astronomy experiments it's quite typical to have many millions of files f

I came here to talk about this. I deal with data management for a bunch of physics and astronomy experiments it's quite typical to have many millions of files for any given experiment (say, 1PB of storage for a medium size experiment, 10 million 100MB files). CERN's experiments would easily have billions of files, so I was thinking 64 bits would be a minimal truncation, but 96 is probably more reasonable.