A method for managing backup data units stored in a data server is provided. The backup data may include a first backup data unit established by copying a source data unit into the data server in response to a data backup command received at a first time point. The method includes: acquiring a specified storage space in response to a data backup command received at a second time point; copying the first backup data unit to the specified storage space in a lightweight copy manner; writing differential data contents between the source data unit presented at the second time point and the source data unit presented at the first time point into the lightweight-copied first backup data unit in the specified storage space; and defining the resulting data stored in the specified storage space as a second backup data unit, wherein the second time point is later than the first time point.