FIGS. 5 through 10 are diagrams illustrating an example of the management information recorded in the memory 16. Though the management information is expressed as various tables in a description below, the management information may be expressed with use of any data structure. In the description below, a configuration of each of the tables is an example, and one table may be partitioned into two or more tables or entirety or portions of two or more tables may form one table.

FIG. 5 illustrates a virtual volume management table that is the management information for management of the virtual volumes 30. The virtual volume management table 500 illustrated in FIG. 5 includes virtual volume IDs 501 for identification of the virtual volumes 30, UDBIDs 502 for identification of the user data blocks 32 that are included in the virtual volume IDs 501, extent IDs 503 for identification of the extents 40 corresponding to the user data blocks 32, entry IDs 504 for identification of the entries 42 corresponding to the user data blocks 32, offsets 505 that are offset values from first logical addresses of the entries 42 in the stripe rows 41, and data lengths 506 of data recorded in the entries 42. In a case where the data reduction processing is carried out by the accelerator 14, the data lengths 506 indicate data lengths of the data having undergone the data reduction processing.