Patent ID: 9454317
Filing Date: 2016-09-27
CPC Classification: G06F

Claim Text:
1. A storage controller in a tiered storage system comprising a first storage device including a first physical volume, and a second storage device including a second physical volume, having a lower access speed than the first storage device, and having a greater storage capacity than the first storage device, the first and second physical volumes each comprising a set of storage areas having a certain size, the storage controller processing an input/output request from a host computer, the storage controller comprising: a logical volume management unit which provides the host computer with a logical volume logically constructed using the first and second physical volumes; a tier management unit which manages the first physical volume as a first tier and the second physical volume as a second tier lower than the first tier; a cache controller which defines part of the set of storage areas of the first physical volume as a set of data areas for storing data, and which defines another part of the set of storage areas of the first physical volume as a set of cache areas for storing cache data, and which causes the set of cache areas to function as a cache for the tiered storage system; and an input/output controller which writes data designated by a write request from the host computer to any one of a data area of the first physical volume and a storage area of the second physical volume, and which reads data designated by a read request from the host computer from any one of a data area of the first physical volume and a storage area of the second physical volume when the data designated by the read request is not in the cache, wherein: the cache controller stores, as cache data, the read data in a cache area of the first physical volume when the read request designates a data read from the second physical volume; the tier management unit determines storage areas storing data to be transferred from the second physical volume to the first physical volume, based on a descending order of access frequencies of the storage areas of the second physical volume; the cache controller redefines, as a first data area, a first storage area of the first physical volume defined as a first cache area, instead of transferring first data stored in a second storage area of the second physical volume to the first physical volume, when the determined storage areas include the second storage area and when the first data is also stored as first cache data in the first cache area; and the tier management unit transfers the first data to a free data area of the first physical volume when the determined storage areas include the second storage area and when the first data is not stored in the cache.