Patent ID: 7752390

Claim:
A disk array apparatus for storing data in a plurality of disk drives, said disk apparatus comprising: a control processor which controls reading and writing of data with respect to a first logical volume which is generated using storage areas the plurality of disk drives, performs control such that data, stored in the first logical volume prior to being updated by the writing of update data into the first logical volume, is copied and written in a second logical volume as differential data for each generation, and manages the differential data by providing a snapshot management table, which manages a relation among differential data for each generation stored in the second logical volume, in an area of a memory, wherein the control processor manages an amount of data stored in the second logical volume, and reduces the capacity of the second logical volume if the amount of data stored in the second logical volume has decreased to be less than a second ratio of the capacity of the second logical volume, wherein, by dividing a pool management table into groups, the control processor manages the first logical volume and the second logical volume for each of the groups, and reduces a capacity of the second logical volume of each of the groups by adding a new logical volume to or deleting a logical volume from the pool management table of each of the groups based on a result of comparison of an amount of data stored in the second logical volume of each of the groups to the capacity of the second logical volume of the group.