Computer system

A computer system that provides a virtual volume to a host, comprising:

• an interface configured to transmit and receive data with the host through a network;
• and
• a control unit configured to control access to a physical storage drive from the host through the interface,
• wherein the control unit is configured to
• manage first mapping information between the virtual volume and a virtual storage region on a virtual storage drive, and second mapping information between the virtual storage region and a physical storage region provided by the physical storage drive, and convert access to the virtual volume to access to the physical storage region according to the first mapping information and the second mapping information,
• form a virtual parity group including a plurality of virtual storage drives,
• store a redundant data set in a virtual stripe array including virtual stripes that are virtual storage regions of a prescribed size of the plurality of virtual storage drives constituting the virtual parity group,
• map the virtual stripes of the virtual stripe array to different physical storage drives,
• form virtual chunks including one or more virtual stripe arrays in the virtual parity group,
• form a plurality of physical parity groups including a plurality of the physical storage drives,
• map the virtual stripes of the one or more virtual stripe arrays from the virtual chunks in a distributed manner to the plurality of physical parity groups,
• select one or more virtual chunks from among the virtual chunks, and
• convert the physical storage regions corresponding to the selected one or more virtual chunks to spare regions in the physical storage region.