Patent ID: 8458424

Claim:
A storage system comprising: a virtual volume including multiple virtual areas; a pool which is a storage area configured of multiple actual area groups of different performances; and a controller, which receives an access command from an access source, and when an actual area has been assigned to a virtual area identified from the access command, accesses the actual area, and when an actual area has not been assigned to the identified virtual area, assigns an actual area of the pool from the pool to the identified virtual area, and accesses the assigned actual area, (A) wherein the controller is configured to manage which actual area is assigned to which virtual area and an access load of the actual area that is assigned to the virtual area, (B) wherein the controller is configured to migrate, when the access load of a first actual area assigned to a first virtual area is inappropriate for a first actual area group comprising the first actual area, data from the first actual area to a second actual area in a second actual area group, and assign the second actual area, instead of the first actual area, to the first virtual area, (C) wherein the controller is configured to manage history information, which indicates at least one of a relationship of each of the multiple virtual areas and a tier of actual area assigned to each of the multiple virtual areas at least one point of time in the past and a relationship of each of the multiple virtual areas and a tier of each of the actual areas which should be ideally assigned to each of the multiple virtual areas in at least one point of time in the past, (D) wherein the controller is configured to perform, in response to receiving an input of a certain point of time in the at least one point of time in the past, data migration between actual areas for achieving data allocation at the certain point of time in the past or ideal data allocation at the certain point of time in the past based on the history information, and wherein the data allocation is the allocation of data in a virtual area to an actual area in an actual area group.