An information system comprises a host computer; a management computer; and a storage system including a storage controller and a plurality of storage volumes, the storage system configured to provide thin provisioned volumes from the plurality of storage volumes to the host computer for input/output. Each thin provisioned volume includes a plurality of segments which are provided by chunks of the storage volumes in the storage system. The storage controller is configured to assign a chunk to a segment on demand, analyze effectiveness of different chunk sizes for a chunk to be assigned to a segment and provide a report of the analyzed effectiveness to the management computer, and determine a size of a chunk to be assigned to a segment based on input from the management computer after the management computer receives the report of analyzed effectiveness.