A storage area, among multiple storage areas, which meets a predetermined requirement is determined to be a target for access. In a controller for controlling a multi-tiered storage subsystem, the following components operate under the control of a file write unit and a file read unit. First, a list acquiring unit obtains a list of tiers that can meet file access requirements. A requisite energy calculating unit calculates an additional energy amount necessary to satisfy file access requirements for each tier, an allowable energy calculating unit calculates an allowable additional energy amount, and a path retrieving unit determines a path to a target tier based on the energy amounts. An identifier acquiring unit obtains a file identifier, and an access point generating unit determines a file access point based on the path and the file identifier. A method for controlling a multi-tiered storage subsystem is also described.