Array type disk system updating redundant data asynchronously with data access

摘要

In a disk array system, data read out and data written anew are temporarily held as former data in a former data holding portion. When a write operation has occurred, a CPU searches the holding portion for write data, it generates update data from the new and former write data items, and it holds the generated update data in an update data holding portion. In addition, the CPU stores the storage address of redundant data associated with the held update data, as log data in a log data holding portion. Further, the CPU operates asynchronously with the write operation to read out the redundant data of the address of the holding portion, to calculate new redundant data from the read redundant data and the held update data, and to write the new redundant data into the address of the log data. On this occasion, a parity area and a data area are separated so as to heighten read/write processing speeds and a parity generation processing speed.