Storage apparatus and storage apparatus control method

A storage apparatus, comprising:

• a storage unit providing a preliminary physical volume thereof and at least one backup physical volume thereof for storing data transmitted from a higher-level device, each of the preliminary and backup physical volumes being formed by a plurality of physical disks;
• and
• a control unit for controlling reading and writing of data from and in a logical volume mapped to at least one physical disk of said preliminary physical volume in response to a read request and a write request from a higher-level device;
• wherein said control unit measures the load status of said logical volume based on a data amount and a command throughput transferred between said higher-level device and said storage unit,
• copies contents of said logical volume from said physical disk of said preliminary physical volume to one or more backup logical volumes mapped to some physical disks of said backup physical volume based on the measurement results of the load status of said logical volume when a load of said logical volume exceeding a default value, associates said logical volume mapped to said preliminary physical volume with said backup logical volumes mapped to said backup physical volume as one virtual volume, and provides said virtual volume to said higher-level device, and
• when a write request involving read processing for reading data from said virtual volume is given from said higher-level device, reads said data from one of said logical volume and said backup logical volumes associated with said virtual volume and writes data from said higher-level device in all said logical volume and said backup logical volumes associated with said virtual volume, and when a read request for reading data from said virtual volume is given, reads corresponding data from one of said logical volume and said backup logical volumes that is associated with said virtual volume and not subject to a most recent read processing.