To generate backup data based on a log while a power consumption of a standby system is reduced, method for data backup is provided in which a first computer system transmits a data update record, a second storage system of a second computer system receives and then stores the data update record, and a second computer of the second computer system generates a copy of data contained in the first computer system based on the stored data update record. The method for data backup includes monitoring the data update record transmitted by the first computer system, and stopping, when a predetermined first condition is satisfied, the second computer; and starting, when a predetermined second condition is satisfied, the second computer, thereby generating the copy of the data contained in the first computer system based on the stored data update record.