A membrane separation device is disclosed along with systems and methods employing the device in blood processing procedures. In one embodiment, a spinning membrane separator is provided in which at least two zones or regions are created in the gap between the spinning membrane and the shell, such that mixing of the fluid between the two regions is inhibited by a radial rib or ridge associated with the spinning membrane that decreases the gap between the spinning membrane and the shell to define two fluid regions, the ridge isolating the fluid in the two regions to minimize mixing between the two. Automated systems and methods are disclosed for separating a unit of previously-collected whole blood into selected blood components, such as concentrated red cells and plasma, for collecting red cells and plasma directly from a donor in a single pass, and for cell washing. Data management systems and methods and priming methods are also disclosed.