In a data management method for a storage device, the storage device includes a nonvolatile memory device including a plurality of memory blocks. A TRIM-after-COPY command is received from an external host such that a data compaction operation is performed on a first storage region. Valid data stored in the first storage region are internally copied into a second storage region based on the TRIM-after-COPY command. A TRIM operation is performed based on the TRIM-after-COPY command to update a logical-to-physical address mapping table and a valid page bitmap.