Patent ID: 8261032

Claim:
A method for backing up data stored in a cache memory, which is performed in a storage system for temporarily storing data from a host device to a cache memory and then writing the data to a storage device, the method comprising steps of: if a consumption ratio, which is a ratio of a total amount of dirty data elements which are stored in a first cache memory in a first control module of a plurality of control modules to a storage capacity of the first cache memory, is greater than or equal to a first predetermined ratio, then dividing the dirty data elements into first dirty data elements and second dirty data elements and copying the second dirty data elements to a second cache memory in a second control module of the plurality of control modules, wherein the dirty data elements are evenly divided according to the total of the number of the first control modules and the number of the second control modules provided where one or more second control modules are provided for each of the first control modules; while power is supplied from a primary power supply, copying the second dirty data elements to the second cache memory; and if power is supplied from a battery after power supplied from the primary power supply stops: backing up the first dirty data elements, which are stored in the first cache memory and are not copied to the second control module, from the first cache memory to a first non-volatile memory in the first control module; backing up the second dirty data elements by the second control unit from the second cache memory to a second non-volatile memory in the second control module; creating management information by the first control module to indicate a cache area, where a dirty data element exists, of the first cache memory and to indicate a control module to which the dirty data element is copied in the control module; writing the management information to the first cache memory; updating the management information as copying of the dirty data element completes; and backing up the management information, in addition to the dirty data element, from the first cache memory to the first non-volatile memory.