Patent ID: 7370145

Claim:
A write back method for making a RAID (i.e., redundant array of independent/inexpensive disk drives) apparatus carry out: an update information storing processing for storing update information of post-update data stored by a cache memory, which has been updated by update data sent from a host computer, in an update information management table; a reference value generation processing, by obtaining the update information of the post-update data from the update information management table, for generating a first reference value expressing a load of a write processing by using a Small Write method, based on the aforementioned update information, and a second reference value expressing a load of a write processing by using a Read & Bandwidth Write method; a write method determination processing, by comparing the first reference value with the second reference value generated by the aforementioned reference value generation processing, for determining a write method out of either the Small Write method or the Read & Bandwidth Write method, based on the comparison result; and a write processing for reading the data stripe of the post-update data which is stored by the cache memory, and updating the data stripe by using a method determined by the write method determination processing.