Patent ID: 8447939

Claim:
A storage control device which provides a higher level device with a first logical volume among first and second logical volumes of a storage device and manages a snapshot of the first logical volume, comprising: a write processing module which, in cases where data elements corresponding to a write target are written to a first storage area in the first logical volume at or after a snapshot acquisition time point, saves pre-update data elements which are stored in the first storage area in the second logical volume, and writes data elements corresponding to the write target to the first storage area; and a read processing module which, in cases where data elements are read from a second storage area of the snapshot of the first logical volume, reads data elements from the storage area in the second logical volume if a storage area in the second logical volume is associated with the second storage area and reads data elements from the storage area in the first logical volume corresponding to the second storage area if a storage area in the second logical volume is not associated with the second storage area, wherein in cases where the write processing module receives a write request corresponding to erasure, and in response to the write request corresponding to erasure, overwrites erasure-corresponding data elements which are data elements corresponding to an erasure target and which are stored in a third storage area in the first logical volume with erasure data elements which are data elements signifying erasure at or after the snapshot acquisition time point, the write processing module associates the third storage area with a fourth storage area in which dummy data corresponding to the erasure-corresponding data elements stored in the third storage area are stored, wherein when receiving a command requesting to erase a data element, old data, which is copied to a different volume during Copy On Write snapshot, is set to be unable to be read and in Copy On Write snapshot, when overwriting, although old data is copied, the old data is substituted with dummy data, and wherein the dummy data is stored one region having a plurality of regions are linked.