Method for backup and storage system

A method for managing backup of data stored in first and second storage devices structuring a mirrored pair, said method comprising:

• at a first time,
• (a) managing whether updating is carried out or not to each of data blocks of said first and second storage devices using first and second update-management tables;
• said data blocks being respectively partitioned in said first and second storage devices;
• and said first and second update-management tables corresponding respectively to said first and second devices and respectively indicating any update to each of said data blocks of said respective first and second storage devices,
• (b) stopping a process of carrying out updating to said second storage device, and
• (c) starting an updating process of said second update-management table to hold the same information as said first update-management table;
• at a second time which is after said first time or at the same time as said first time,
• (d) stopping said updating process of said second update-management table,
• (e) resetting said first update-management table to a state in which no update has been carried out to the data blocks of said first storage device, and
• (f) copying, to a backup medium, data of said second storage device stored in at least one of said data blocks indicated by said second update-management table as being updated;
• and
• at a third time which is after said second time,
• (g) copying data of said first storage device stored in at least one of said data blocks indicated by said second update-management table as being updated to at least one of data blocks of said second storage device corresponding to said data blocks of said first storage device, and
• (h) then making contents of said second update-management table coincide with contents of said first update-management table.