Patent ID: 8495293

Claim:
A storage system, comprising: one or more logical volumes, which has at least one of a primary volume and a secondary volume, which constitutes a volume pair together with the primary volume; and a controller, which writes a data element stored in the primary volume to the secondary volume, which constitutes a volume pair with the primary volume, in accordance with a selected storage mode, which is a data storage mode selected from a plurality of types of data storage modes, wherein the controller switches the selected storage mode from the currently selected type of data storage mode to a type of data storage mode that differs therefrom, wherein the controller, upon receiving an I/O command from a computer, accesses a logical volume specified by this I/O command and the storage area thereof, changes a type of the secondary volume from the type corresponding to the pre-switch data storage mode to the type corresponding to the post-switch data storage mode by carrying out specified processing for respective storage areas constituting the secondary volume conforming to the pre-switch data storage mode when switching the selected storage mode, and executes the selected storage mode switching while receiving an I/O command from the computer, and when the I/O command received from the computer is a write command, controls writing of the write-targeted data element conforming to this write command based on whether or not the write destination specified by this write command is a primary volume or a pre-switch secondary volume, and whether or not the write-destination storage area is a storage area for which the specified processing has been completed.