A data backup method, which is performed by a backup server, wherein the method comprises: sending a change information obtaining request to a file server, after a data backup is triggered, wherein the change information obtaining request is used to request change information of data in the file server; receiving a record of a data change between a second snapshot and a first snapshot, that is returned by the file server, where the first snapshot is created before the second snapshot, the data change record is used to record information about a data block corresponding to the change between the second snapshot and the first snapshot, and the data change record includes identification information of the changed data block; obtaining, from the file server based on the data change record, data in the data block identified by the identification information of the data block; storing the obtained data in a backup storage device; and establishing a data mapping relationship for the data backup, where the data mapping relationship includes identification information of all data blocks in the second snapshot, storage locations of all the data blocks in the second snapshot in the backup storage device, and a snapshot identifier of the second snapshot, wherein the data mapping relationship is stored in the backup storage device; wherein the data change record further includes a corresponding operation identifier, and wherein the establishing a data mapping relationship comprises: copying a data mapping relationship established during a previous backup into the backup storage device, and modifying the copied data mapping relationship based on the data change record, to obtain the data mapping relationship for the data backup; and wherein before sending a change information obtaining request to a file server, the method further comprises sending a snapshot request to the file server; receiving a snapshot creation success response returned by the file server, where the response comprises the snapshot identifier of the second snapshot. sending a change information obtaining request to a file server, after a data backup is triggered, wherein the change information obtaining request is used to request change information of data in the file server; receiving a record of a data change between a second snapshot and a first snapshot, that is returned by the file server, where the first snapshot is created before the second snapshot, the data change record is used to record information about a data block corresponding to the change between the second snapshot and the first snapshot, and the data change record includes identification information of the changed data block; obtaining, from the file server based on the data change record, data in the data block identified by the identification information of the data block; storing the obtained data in a backup storage device; and establishing a data mapping relationship for the data backup, where the data mapping relationship includes identification information of all data blocks in the second snapshot, storage locations of all the data blocks in the second snapshot in the backup storage device, and a snapshot identifier of the second snapshot, wherein the data mapping relationship is stored in the backup storage device; wherein the data change record further includes a corresponding operation identifier, and wherein the establishing a data mapping relationship comprises: copying a data mapping relationship established during a previous backup into the backup storage device, and modifying the copied data mapping relationship based on the data change record, to obtain the data mapping relationship for the data backup; and wherein before sending a change information obtaining request to a file server, the method further comprises sending a snapshot request to the file server; receiving a snapshot creation success response returned by the file server, where the response comprises the snapshot identifier of the second snapshot. copying a data mapping relationship established during a previous backup into the backup storage device, and modifying the copied data mapping relationship based on the data change record, to obtain the data mapping relationship for the data backup; and wherein before sending a change information obtaining request to a file server, the method further comprises sending a snapshot request to the file server; receiving a snapshot creation success response returned by the file server, where the response comprises the snapshot identifier of the second snapshot.