Computer system for load balance, program and method for setting paths

A system comprising:

• a computer having a first host bus adapter (HBA) and a second HBA;
• and
• a storage system having a first logical unit, a first channel adapter (CHA) and a second CHA related to the first logical unit, the first CHA and the second CHA being coupled to the first HBA and the second HBA via a network, the first HBA being coupled to the first logical unit by a first access path including the first CHA and by a second access path including the second CHA, and the second HBA being coupled to the first logical unit by a third access path including the first CHA and by a fourth access path including the second CHA,
• wherein the computer selects the first access path as an active path and accesses the first logical unit by using the first access path,
• wherein the computer checks whether or not the second HBA has a second load smaller than a first load of the first HBA, and changes the active path into the third access path if the second HBA has the second load that is smaller than the first load,
• wherein the computer accesses the first logical unit by using the third access path after changing the active path,
• wherein the first CHA has a cache memory for temporarily storing data which is to be stored into the first logical unit in the storage system or be sent from the storage system, and
• whereby the computer can continue to use the cache memory after changing the active path from the first access path to the third access path.