Patent ID: 7590884

Claim:
A storage system, comprising: a plurality of disk devices configured as a redundant system, a control unit which performs reading and writing of data from and to said each disk device according to requests from a higher-level apparatus, wherein said control unit comprises: a cache memory which stores data of each said disk device; and a processing unit which read-accesses each said disk device and receives read data and a response result from each said disk device, wherein said processing unit: when the response to the read access of one of said disk devices is a recovered read error response, performs retry read access of same data on another of said disk devices constituting said redundant system, discriminates whether the response from said disk device accessed by said retry read does not include an error, and judges the read data obtained from said retry read access to be valid, and after executing said retry read access, performs read access of said one disk device with usage of the cache memory of said disk device disabled, receives read data, compares the read data with read data from said another disk device, and executes diagnostics of said one disk device.