Combined disk array controller and cache control method for parity generation mode and data restoration mode

Abstract

Upon receiving an access command designated with a parity generation mode from a main controller upon update data transfer from a host apparatus, a cache controller reads out update data from that location in a block in an update data area in a cache memory, which is designated by the command, and writes the readout data in a FIFO memory. The cache controller then reads out data before update from that location in a block in a data before update area, which is present in an identical block column, EX-ORs the readout data and the contents stored in the FIFO memory, and writes the obtained EX-OR in the FIFO memory. The cache controller reads out parity before update from that location in a block in a parity before update area, which is one block ahead of the block in the data before update area, and EX-ORs the readout parity and the contents of the FIFO memory to generate parity data.