Just some ambiguity there. Your example of linear growth is incorrect. You state that the database starts at 100GB and grows at 10% per year for 2 years. That gives it a size of 100 * 1.1 = 110GB for the end of the first year and 110 * 1.1 = 121GB for the end of the second year. Percentage growth plans are always exponential, never linear. If your target growth is by a certain number of MB (or GB) per year then the growth plan should be specifiying MB (or GB) and not a percentage.