Patent ID: 8117409

Claim:
A method of reading and writing data in an information system, comprising: providing a storage apparatus having one or more disk drives and a controller for providing a volume for storage, the volume being logically divided into multiple segments to which physical storage areas on the one or more disk drives are able to be independently allocated; in a read process, reading a data image by reading data if a physical storage area has been allocated to a designated segment for the data and reading a default data pattern if a physical storage area has not been allocated to a designated segment for the data; in a write process, writing the data image by writing data to a designated segment if a physical storage area has been allocated to the designated segment, not allocating a physical storage area for the data if the data does equal the default data pattern, and allocating a physical storage area for the data if a physical storage area has not been allocated to a designated segment for the data and if the data does not equal the default data pattern; and in a backup process, copying the data of the volume, including the data having the default data pattern for respective segments which have not been allocated physical storage areas, to a backup storage, wherein a storage capacity for the written data image in the volume is smaller than a storage capacity for the read data image, wherein the volume has a standard mode and a restore mode, the method further comprising: in the standard mode, when a write command is received, allocating a physical storage area from the one or more disk drives to a designated segment of the volume if a physical storage area has not been allocated to the designated segment and if data corresponding to the write command does not equal the default data pattern, and in the standard mode, storing the data associated with the write command in the physical storage area if the physical storage area is allocated to the designated segment of the volume, or in the restore mode, discarding a received data from the backup storage associated with the write command if a physical storage area has not been allocated to the designated segment and if the received data does equal the default data pattern, and writing the received data from the backup storage if a physical storage area has been allocated.