Patent ID: 7904683

Claim:
A storage system including a host system, a first storage apparatus having a primary volume group to be connected to said host system, and a second storage apparatus having a secondary volume group, and which duplicates data by connecting said second storage apparatus to said host system and said first storage apparatus, and configuring a pair with said primary volume group and said secondary volume group, wherein said first storage apparatus comprises: a first mapping table for storing first mapping information which associates first information that specifies the respective primary volumes in said primary volume group and second information that specifies the respective secondary volumes in said secondary volume group; and a first control unit for writing first data in a relevant primary volume upon receiving from said host system a command for writing said first data in any one of the primary volumes in said primary volume group, and sending to said second storage apparatus a first command for writing said first data in a secondary volume corresponding to the primary volume to be written with said first data specified using said first mapping information; and wherein said second storage apparatus comprises: a second mapping table for storing second mapping information associated with the same contents as said first mapping information; a second control unit for writing second data in a relevant secondary volume upon receiving from said host system a command for writing said second data in any one of the secondary volumes in said secondary volume group, and sending to said first storage apparatus a second command for writing said second data in a primary volume corresponding to the secondary volume to be written with said second data specified using said second mapping information; and wherein said second storage apparatus comprises a table for storing information showing whether it is a primary apparatus or a secondary apparatus; and wherein said second control unit sends to said host system first information specifying a primary volume in said primary volume group specified with said second mapping information in substitute for second information that specifies the respective secondary volumes in said secondary volume group when a device online request is issued from said host system and information showing that it is a secondary apparatus has been set.