A data management system respectively computes first hash values while sliding a window a prescribed amount at a time with respect to a prescribed range from a start location of a data block to a prescribed size. The system extracts, from among the first hash values, a first hash value, which is equivalent to a characteristic value, and partitions the data block into a first chunk of data at a location corresponding to this first hash value. The system determines coincidence between a first chunk of data and a stored second chunk of data, and prevents duplicate data from being stored twice.