Patent ID: 8041910

Claim:
A storage apparatus including a first volume for storing data sent from a host apparatus and for performing backup of the first volume, comprising: a plurality of disk drives; and a control unit providing a first volume and a second volume to the host apparatus, each of the first volume and the second volume being defined by a plurality of segments on the plurality of disk drives, wherein the control unit creates a second volume as a backup volume of the first volume upon receiving a backup command regarding the first volume from the host apparatus, and sends a completion reply responsive to the backup command to the host apparatus while formatting of the second volume and replication from the first volume to the second volume are incomplete, wherein after sending the completion reply responsive to the backup command, and upon receiving a write command to write to a first segment of the first volume, the control unit: sends a completion reply responsive to the write command after storing data of the write command to a cache memory; makes a determination as to whether data of the first segment is replicated based on a replication management bitmap; when the determination indicates that data of the first segment is not replicated, sets a write inhibition flag corresponding to the first segment to “ON”, replicates the data of the first segment to the second segment in the second volume corresponding to the first segment, changes the write inhibition flag corresponding to the first segment to “OFF”, and writes the data of the write command stored in the cache memory to the first segment; and when the determination indicates that the data of the first segment is replicated, writes the data of the write command stored in the cache memory to the first segment.