Abstract: To directly and smoothly execute data update on a duplication volume while suppressing a load on a master volume, when performing backup by employing the snapshot system. The duplication system includes: duplication volumes for a master volume; a shared volume for storing duplication data of the duplication volumes; and a main control unit which manages data accesses made from a host computer to the duplication volumes and manages data storing places. The main control unit includes a data duplication control module having a function which duplicates data of the master volume to the duplication volumes when updating the master volume, and directly performs data update to each of the duplication volumes when updating the duplication volumes.

Abstract: A disk apparatus includes a second volume to which data of a first volume is copied, a third volume which stores a snapshot of the first volume, and an I/O processing unit which reads out data from the third volume when data of an area in which difference data exists in the third volume is read out, when data of an address in which the difference data does not exist in the third volume is read out, reads out data from the first volume if data copying from the first volume to the second volume has not been completed, and reads out data from the second volume if the data copying has been completed.

Abstract: To directly and smoothly execute data update on a duplication volume while suppressing a load on a master volume, when performing backup by employing the snapshot system. The duplication system includes: duplication volumes for a master volume; a shared volume for storing duplication data of the duplication volumes; and a main control unit which manages data accesses made from a host computer to the duplication volumes and manages data storing places. The main control unit includes a data duplication control module having a function which duplicates data of the master volume to the duplication volumes when updating the master volume, and directly performs data update to each of the duplication volumes when updating the duplication volumes.

Abstract: A disk apparatus includes a second volume to which data of a first volume is copied, a third volume which stores a snapshot of the first volume, and an I/O processing unit which reads out data from the third volume when data of an area in which difference data exists in the third volume is read out, when data of an address in which the difference data does not exist in the third volume is read out, reads out data from the first volume if data copying from the first volume to the second volume has not been completed, and reads out data from the second volume if the data copying has been completed.

Abstract: It is to provide a data storage system which causes no delay in the access performance of a master volume in the snapshot action of a disk array subsystem. The data duplication system comprises a temporary data duplication control device and a data duplication control device. The temporary data duplication device functions in such a manner that the master volume and a buffer volume that is built between the master volume and a snapshot volume keep the same volume image. The data duplication control device functions to minimize the I/O load upon the master volume by switching the master volume and the buffer volume as appropriate as the actual data reference target of the snapshot volume.

Abstract: It is to provide a data storage system which causes no delay in the access performance of a master volume in the snapshot action of a disk array subsystem. The data duplication system comprises a temporary data duplication control device and a data duplication control device. The temporary data duplication device functions in such a manner that the master volume and a buffer volume that is built between the master volume and a snapshot volume keep the same volume image. The data duplication control device functions to minimize the I/O load upon the master volume by switching the master volume and the buffer volume as appropriate as the actual data reference target of the snapshot volume.