Patent ID: 7779202

Claim:
An array controller for controlling a disk array with redundancy including at least two disk drives, comprising: a read/write control unit which controls read/write access to the disk drives of the disk array; error counters provided for the respective disk drives, the error counters counting respective numbers of errors if errors occur when the disk drives are accessed; a failure estimation unit configured to detect, as a disk drive which is very likely to fail, a disk drive included in the disk array and having a high error occurrence degree based on the numbers of errors counted by the error counters; and a mode-setting unit which sets the detected disk drive in (i) a first mode that separates the detected disk drive from the disk array when the detected disk drive is considered to have failed and is inaccessible and (ii) a second mode in which the detected disk drive is maintained as an accessible member of the disk array and is controlled by the read/write control unit to prevent reading of data from the detected disk drive of the disk array.