A solution to deduplication in a storage system is disclosed herein. In this solution, a controller stores, at a first storage address, a data block that is written for the first time, and inserts, in a fingerprint table, a first fingerprint of first data that is written for the first time, but does not establish a mapping relationship between the first fingerprint and the first storage address. When receiving subsequently written second data to be written, the controller allocates a second storage address to the duplicate second data, stores the second data at the second storage address, and establishes a mapping relationship between the first fingerprint and the second storage address in the fingerprint table. This reduces an amount of data in the fingerprint table.