In some examples, a client system, in response to a request to modify a first data page at a memory server in a remote access by a client over a network, sends, to the memory server, a request to update a data modification tracking structure stored by the memory server to indicate that the first data page is modified. The client system initiates an incremental data backup from the memory server to a backup storage system of data pages indicated as modified by the data modification tracking structure stored at the memory server.