A distributed storage system includes an edge system including edge nodes, and a core system, which is coupled to the edge system via a network, and is configured to hold backup data of the edge system. Each of the edge nodes is configured to provide a volume to a host, generate XOR update differential data representing a differential between a first generation snapshot of the volume and an old generation snapshot of the volume, the old generation being older than the first generation, and transmit the generated XOR update differential data to the core system. The core system is configured to hold, as the backup data, erasure codes generated based on pieces of XOR update differential data transmitted from the edge nodes, and update the erasure codes based on the pieces of XOR update differential data received from the edge nodes.