Maintaining correct I/O statistics for altered data migrated within a tiered storage environment

A method for maintaining I/O statistics in a tiered storage environment includes maintaining, by a tiered storage layer within a storage system, I/O statistics for data storage elements or areas within the storage system. The tiered storage layer migrates data between storage tiers in accordance with the I/O statistics. A data services layer, that operates independently from the tiered storage layer, alters (e.g., compresses, decompresses) selected data within the storage system and generates a message to the tiered storage layer describing the alteration. The message identifies the selected data, how the selected data before the alteration maps to the selected data after the alteration, and an operator (e.g., percentage) to be applied to I/O statistics associated with the selected data as a result of the alteration The tiered storage layer receives this message and modifies its internal I/O statistics accordingly. A corresponding system and computer program product are also disclosed.