Note that at 128 bits per GUID (not including any storage overhead), 2.7x10^18 GUIDs would take up 43.2 exabytes of storage. That's about 10 million 4TB drives

Note that at 128 bits per GUID (not including any storage overhead), 2.7x10^18 GUIDs would take up 43.2 exabytes of storage. That's about 10 million 4TB drives. It's going to be a while before the birthday paradox is really going to be problematic.