It is provided a storage system including a storage device for storing data, and a controller for controlling data read/write in the storage device. The controller includes a processor for executing a program, and a memory for storing the program that is executed by the processor. The processor executes deduplication processing for converting a duplicate part of data that is stored in the storage device into shared data, and calculates a distributed capacity consumption, which represents a capacity of a storage area that is used by a user in the storage device, by using a size of the data prior to the deduplication processing and a count of pieces of data referring to the shared data that is referred to by this data.