Patent ID: 7146526

Claim:
A data I/O system comprising: a plurality of storage devices; and a controller which controls said storage devices, wherein said controller includes: a read/write unit, responsive to the subsequent receipt of a read request and a write request, for reading data stored in said storage devices and writing data in said storage devices; a logical volume management unit configured to map between a logical image of the data storage of a host processor (logical volume) and an actual space in said storage devices; a volume management unit configured to manage an active primary production volume (P-VOL) and a secondary mirror volume (S-VOL) group including multiple S-VOLS created as mirror images of said primary volume; and an S-VOL restoring unit configured to restore the data of a first S-VOL belonging to the S-VOL group with the data of a second S-VOL belonging to the S-VOL group depending on the type of an error that happens in the first S-VOL; wherein said controller further includes: an access management unit configured to render at least one of said S-VOLs belonging to an S-VOL group read-only as at least one Read-only (RO) S-VOL and rendering at least one of said S-VOLs belonging to an S-VOL group read-and-writable as at least one Read-and-Writable (RW) S-VOL; and an increments management unit configured to store updates that have occurred in a Read-and-Writable (RW) S-VOL since a P-VOL and the RW S-VOL were separated in an increments-volume, wherein said S-VOL restoring unit recovers a RW S-VOL belonging to the S-VOL group by replacing the RW S-VOL with the at least one Read-only (RO) S-VOL that has been updated by data of the increments-volume of the RW S-VOL as an error happens in the RW S-VOL.