A storage controller includes a processor and a memory to store first management information indicating data writing to each of a plurality of logical blocks, corresponding to a plurality of physical blocks of a storage device. The processor is configured to receive a write request to write data to a first logical block and assign a first physical block to the first logical block. The processor is also configured to record in the first management information that data has been written in the first logical block, identify a second logical block in which data has been written, write the addresses of the plurality of physical blocks as second management information, read an address of a second physical block assigned to the second logical block from the second management information, and release the second physical block. The memory may store third management information indicating the number of assignments to each logical block in a plurality of logical volumes corresponding to a storage area, and assign a physical block to a logical block so as to remove duplicate data, or de-duplicate data, in the storage area. A bit map may be stored as the first management information.