Right, but the entire point is that 64 bits is PLENTY. The default block size is 128KB. So 2^64 * block size = 2417851639229258349412352 bytes Or 2147483648

Right, but the entire point is that 64 bits is PLENTY. The default block size is 128KB. So 2^64 * block size = 2417851639229258349412352 bytes Or 2147483648 PB. Sure there might be distributed systems that are mind boggling large, but those aren't in a single filesystem attached to a single node. ZFS would be a better filesystem with "only" 64 bit blocks. Today's higher density nodes are something like 48 disks * 12TB, so approximately 2 per PB. 12 per rack would be 6PB. So 178,956,970 racks consuming 300 times the annual production on earth and you'd start wishing for that 65th bit. All in a single OS connecting to a single storage system. Or you could assume that in the next few decades you'd be batshit crazy to want to install that much storage on a single zfs system and half the overhead of every pointer into the filesystem.