Patent ID: 8732421

Claim:
A storage system comprising: a virtual volume, which is a virtual logical volume comprising multiple virtual areas; a pool, which is a storage area comprising multiple actual area groups having different access performance; and a controller, which stores a corresponding relationship between the virtual area and the actual area, configured to access the actual area corresponding to the virtual area based on accesses to the virtual area, wherein the controller is configured to: (X) decide, based on an access load trend with respect to each virtual area in each time slot, an ideal actual area allocation destination for the each virtual area in the each time slot; and (Y) carry out a reallocation process for reallocating the virtual area to the ideal actual area starting at an actual reallocation start time, which is a time prior to a start time of the each time slot, so that the ideal actual area is allocated to the each virtual area by the start time of the each time slot, and wherein, a preliminary reallocation start time is set to a current time, when a cumulative access load of a first virtual area during a time period from a start time of a first time slot to the current time becomes equal to or larger than a cumulative access load of the first virtual area during a time period of the entire first time slot at a past time, and the current time is a time within the first time slot, wherein a scheduled reallocation start time is a time that is scheduled to start the reallocation process such that the reallocation process can be completed by a start time of a next time slot of the first time slot, and wherein in the (Y): (A) when the preliminary reallocation start time is earlier than the scheduled reallocation start time, the preliminary reallocation start time is the actual reallocation start time for starting the reallocation process; and (B) when the preliminary reallocation start time is either identical to or later than the scheduled reallocation start time, the scheduled reallocation start time is the actual reallocation start time for starting the reallocation process.