Storage apparatus and power saving method thereof

A power saving method of a storage apparatus connected to a host system for sending and receiving data to and from said host system, comprising:

• a first step of a first data storage unit of a plurality of data storage units storing write data requested by said host system;
• a second step of an access history storage unit storing, when there is a write request for writing data into said first data storage unit or a read request for reading data stored in said first data storage unit, history of said write request or read request as access history;
• a third step of an operational information storage unit storing operational information showing whether said first data storage unit is operating;
• a fourth step of an access prediction unit predicting whether said first data storage unit will be accessed based on said access history;
• a fifth step of an operational control unit performing operational control of pre-starting said first data storage unit when said first data storage unit is shut off and said access prediction unit predicts that said first data storage unit will be accessed, or stopping said first data storage unit when said first data storage unit is operating and said access prediction unit predicts that said first data storage unit will not be accessed;
• and
• a sixth step of delaying an error message for a given length of time when said first data storage unit is shut off and there is a read request for reading data stored in said first data storage unit.