Disk array device with selectable method for generating redundant data

A disk array apparatus for storing data used for a higher level device, comprising:

• a plurality of disk drives for storing write data from said higher level device and storing redundant data used for the data of a data group to which the write data from said higher level device belongs;
• a disk control device for transferring the write data between said higher level device and one of said disk drives;
• a redundant data generating circuit present in said disk control device, for generating new redundant data from either (1) the write data from said higher level device, old data to be updated by the write data, and redundant data of the data group to which the write data belongs, or (2) the write data from said higher level device and data not to be updated by the write data of the data group to which the write data belongs;
• and
• a processor present in said disk control device, capable of selecting an operation of said redundant data generating circuit in accordance with at least a comparison by said processor of a number of access times to said disk drives needed for a case where (1) the new redundant data is generated from the write data from said higher level device, the old data to be updated by the write data, and the redundant data of the data group to which the write data belongs, and for a case where (2) the new redundant data is generated from the write data from said higher level device and the data not to be updated by the write data of the data group to which the write data belongs.

A disk array apparatus for storing data used for a higher level device, comprising:

• a plurality of disk drives for storing write data from said higher level device and storing redundant data used for the data of a data group to which the write data from said higher level device belongs;
• a disk control device for transferring the write data between said higher level device and one of said disk drives;
• a redundant data generating circuit present in said disk control device, for generating new redundant data from either (1) the write data from said higher level device, old data to be updated by the write data, and redundant data of the data group to which the write data belongs, or (2) the write data from said higher level device and data not to be updated by the write data of the data group to which the write data belongs;
• and
• a processor present in said disk control device, for selecting an operation of said redundant data generating circuit in accordance with whether said processor detects that a redundant data update operation has succeeded or failed.