In a data backup method performed in a storage system having multiple storage devices, a first storage device having a first LUN queries data consistency points from a second storage device that has a second LUN which has an active-active relationship with the first LUN. The second storage device obtains the data consistency points based on the IO data status record of the first LUN and an IO data status record of the second LUN stored in the second storage device, and provides the data consistency points to the first storage device. The first storage device then creates a snapshot for the first LUN based on the data consistency points, provides differential data between the current snapshot and a previous snapshot, and stores the differential data in the backup storage device.