An information processing system retains one or more files utilized by an external apparatus, each of which is made up of a plurality of chunks, in a manner that the chunks making up each of the files are distributed. The information processing system includes a plurality of chunk servers, each storing chunks, and one master server communicatively coupled thereto. The master server retains a file name of a file, chunk IDs indicating chunks making up the file, and chunk IDs indicating chunk servers storing the chunks. When a snapshot taking request for a file is received, the master server identifies chunks included in the file from the file name and the chunk IDs to instruct the chunk servers having these chunks to take a differential snapshot of each of the chunks with the use of a differential snapshot function included in a local file system of each of the chunk servers.