Patent ID: 7395388

Claim:
A load balancing system for balancing loads of storage apparatuses therein, comprising: a first apparatus equipped with at least one internal logical device and configured to provide a plurality of virtual logical devices accessible for a host system, said virtual logical devices being physically located on an external storage apparatus while virtualized as internal logical devices of the first apparatus to the host system 1 , data of at least one virtual logical device being maintained as a mirror-copy pair with another virtual logical device among the virtual logical devices therein; a second apparatus equipped with at least one internal logical device and configured to selectively provide a plurality of virtual logical devices accessible for a host system; and a management device that periodically detects a load of said first apparatus and a load of said second apparatus, respectively, and migrates a virtual logical device that is not maintained as a mirror-copy pair with any other virtual logical devices in said first apparatus to said second apparatus when the load of said first apparatus is greater than the load of said second apparatus.