When a data backup apparatus is powered on, a quantity of dead blocks and a quantity of live blocks are counted. After the data backup apparatus is powered off, a proportion occupied by dead blocks corresponding to each sequence access identifier at the power-on time point in a total quantity of sampled cache blocks corresponding to the sequence access identifier, is calculated according to the counted quantities of dead blocks and live blocks that correspond to the sequence access identifier at the time point when the data backup apparatus is powered on. The calculated proportion is compared with a preset threshold, and a dead block in a volatile memory unit is predicted according to a comparison result. During backup, a cache block that is predicted to be a dead block is not backed up.