1. A method for deduplication in a memory system using data association information, comprising: extracting information about a target file and at least one reference file associated with the target file as association information before duplication determination is performed; identifying the at least one reference file using at least the association information as a comparison target set for comparison at substantially the same time as the duplication determination of the target file is performed; and performing the duplication determination with the target file with respect to the at least one reference file in the selected comparison target set.