In a large-scale storage system configured by combining a plurality of storage modules, it is possible to improve a read performance for deduplicated data. A large-scale storage system includes a first storage module and a second storage module each connected to a computing machine, the first storage module and the second storage module being connected to each other by a network, the first controller determines whether second data that is same as first data requested to be written is already stored in the second storage module when the first storage module receives a write request from the computing machine, and the first controller determines whether to store the first data in the first storage medium or to refer to the second data in the second storage module in a case in which the second data is already stored in the second storage module.