Storage system with storage controllers to control data input and output between a host apparatus and a storage drive in normal and degraded operation states

A method of controlling a storage system including a plurality of storage controllers,

• the plurality of storage controllers being configured to shift from a normal operation mode to a degraded operation mode in accordance with a command from a management apparatus,
• each of the plurality of storage controllers being configured to change from state to state among a plurality of states,
• the plurality of states including:
• a normal operation state in which the storage controller controls data input and output between one or more host apparatuses and one or more storage drives under the normal operation mode;
• a degraded operation state in which the storage controller controls data input and output between one or more host apparatuses and one or more storage drives under the degraded operation mode;
• and
• a standing-by state in which the storage controller stops data input and output between a host apparatus and a storage drives, consuming less power than in the normal operation state or the degraded operation state, and
• the method comprising:
• making, in the normal operation mode, each of the plurality of storage controllers work in the normal operation state:
• making, in transition from the normal operation mode to the degraded operation mode in accordance with a command from the management apparatus, a storage controller designated by the management apparatus out of the plurality of storage controllers change from the normal operation state into the standing-by state and the other storage controllers except for the designated storage controller change from the normal operation state into the degraded operation state;
• and
• making the storage controller in the standing-by state change into the degraded operation state in response to stop of a storage controller in the degraded operation state because of occurrence of a failure under the degraded operation mode,
• wherein the plurality of storage controllers are included in a module,
• wherein the number of storage controllers included in the module is four,
• wherein the module includes a first node and a second node,
• wherein two of the four storage controllers are included in the first node and the other two of the four storage controllers are included in the second node, and
• wherein the four storage controllers are able to control data input and output between a common host apparatus and a common storage drive in the normal operation state and the degraded operation state.