COMPUTER SYSTEM HAVING TIERED BLOCK STORAGE DEVICE, STORAGE CONTROLLER, FILE ARRANGEMENT METHOD AND STORAGE MEDIUM

According to one embodiment a storage controller includes a mode switching unit, a data input/output controller and a data arrangement controller. The mode switching unit switches a first mode to a second mode in accordance with a mode switching request from a host device based on a tier arrangement rule. The data input/output controller accesses a first sequence of blocks constituting a first file indicated by a tier arrangement rule, when the host device requests access to a logical address range storing the first sequence of blocks. The data arrangement, controller transfers, to a storage area of a tier designated by the tier arrangement rule, data in an extent including a sequence of blocks located in a logical address range accessed in the second mode.