A rack storage system comprising storage racks (12a, 12b), which have storage places for loads in rack levels situated one above the other, and a load manipulation unit (4; 4'; 4"), which has at least one first load-lifting device, comprising a liftable and lowerable transport device for storing and retrieving loads, as well as a first buffer device for temporarily storing loads on the provisioning conveyors (43, 44) thereof, and at least one rack aisle extending between the storage racks (12a, 12b) and along the load-lifting device and buffer device, and guide tracks running in at least some of the rack levels in longitudinal direction of the rack aisle, and at least one single-level rack operating device, which can be displaced along the guide tracks for transporting loads between the storage places and the buffer device as well as a conveying system connected to the load-lifting device, comprising a first conveying system (54a; 69) for transporting loads to the load-lifting device, and a second conveying system (55a; 71) for removing loads from the load-lifting device, wherein, in at least some of the rack levels, the buffer device comprises a fixed first buffer path section and fixed second buffer path section, in which the provisioning conveyors (43, 44) are arranged, and between which the transport device of the load-lifting device can be positioned at least in some of the rack levels and driven in such a manner that at least a first load can simultaneously be conveyed from the first buffer path section to the transport device and the transport device convey at least a second load to the second buffer path section, wherein the first buffer path section comprising the provisioning conveyors and the second buffer path section comprising the provisioning conveyors are provided relative to the rack aisle in front of and behind the load-lifting device as well as laterally next to the rack aisle along the guide tracks, and wherein the first buffer path section serves exclusively for a retrieval process for loads and the second buffer path section serves exclusively for a storage process for loads, characterized in that the guide tracks run in longitudinal direction of the rack aisle along the storage racks (12a, 12b), the load-lifting device and the buffer device and that the load-lifting device arranged between the conveying devices (54a, 55a; 69, 71) and the buffer path sections (41a, 42a) comprising the liftable and lowerable transport device for storing and retrieving loads is also provided laterally next to the rack aisle along the guide tracks, wherein the provisioning conveyors in the first buffer path section are provided in the form of accumulating tracks conveying the loads from the pick-up section remote from the load-lifting device to a transfer section adjacent to the load-lifting device in one single, non-reversible conveying direction, wherein the pick-up section can be approached by the single-level rack serving device and the single-level rack serving device can relocate a load to the pick-up section, and wherein the provisioning conveyors in the second buffer path section are provided in the form of accumulating tracks conveying the loads from a pick-up section adjacent to the load-lifting device to the transfer section remote from the load-lifting device in one single, non-reversible conveying direction, wherein the transfer section can be approached by the single-level rack serving device and the transfer section can relocate a load to the single-level rack serving device.