Proposed are a storage system and a data storage method capable of automatically and flexibly changing the redundant destination of data, and verifying the authenticity of data when a system is changed. A primary storage apparatus includes a search unit for searching a secondary storage apparatus for storing the redundant data, and a primary creation unit for creating primary-side authentic information showing that the data is authentic. A secondary storage apparatus includes a secondary creation unit for creating secondary-side authentic information showing that the redundant data is authentic. This storage system also includes a primary storage unit for storing the data in a storage extent of the primary storage apparatus and a secondary storage unit for storing the redundant data in a storage extent of the secondary storage apparatus when the primary-side authentic information and the secondary-side authentic information coincide.