[sacrilicious]

Total conjecture, but 3 ways come to mind: De-duplication, compression, and hierarchical storage management. Keep less-frequently accessed parts of the data 'Nearline', and snapshot the lower-demand, older data slightly less often. Continuous data protection appliances were probably designed and tuned specifically for this problem set, and one could assume it was built into the original architecture so that an appropriate amount of the infrastructure already had backup space in mind and accounted for.