In one embodiment, a method includes monitoring data usage on a per-extent basis for data stored to a first location in a first tier of a multi-tier file system and data stored to a second location in a second tier of the multi-tier file system. The method also includes swapping data usage statistics for the data stored to the first location with data usage statistics for data stored to the second location in response to a determination that data usage of the data stored to the second location is not accounted for in the data usage statistics for the data stored in the first location after a first portion of the data stored to the first location is swapped with a second portion of the data stored to the second location. Moreover, data blocks which are swapped within a same extent do not have data usage statistics thereof swapped.