Patent ID: 8387063

Claim:
A storage apparatus having a plurality of physical devices for balancing and retaining divided data and parity of said data, in which data sent from a host computer is divided and stripped across the plurality of physical devices, comprising: a load ratio calculation unit for calculating an operating ratio of said plurality of physical devices, wherein the operating ratio indicates a work load on a physical device; a load ratio determination unit for determining whether said operating ratio of said plurality of physical devices calculated by said load ratio calculation unit is equal to or greater than a first threshold value; a command ratio determination unit for determining whether a write command ratio on each of the plurality of physical devices or a read command ratio on each of the plurality of physical devices is equal to or greater than a second threshold value, when said load ratio determination unit determines that said operating ratio of at least one of said plurality of physical devices is equal to or greater than said first threshold value, wherein the write command ratio is a number of write commands to a number of read commands issued from said host computer and the read command ratio is a ratio of said number of read commands to said number of write commands issued from said host computer; a change unit for changing said parity retained in said at least one of said plurality of physical devices, and data retained in another physical device of said plurality of physical devices, so as to lower a ratio for retaining parity of said at least one of said plurality of physical devices determined by said load ratio determination unit as being equal to or greater than said first threshold value, when said command ratio determination unit determines that said write command ratio is equal to or greater than said second threshold value, wherein said change unit changes data retained in said at least one of said plurality of physical devices, and parity retained in said another physical device of said plurality of physical devices so as to raise said ratio for retaining said parity of said at least one of said plurality of physical devices determined by said load ratio determination unit as being equal to or greater than said first threshold value, when said command ratio determination unit determines that said read command ratio is equal to or greater than said second threshold value, wherein the change unit lowers or raises the ratio by moving the parity from one physical device to another.