A rack storage system, comprising a rack storage with storage racks (12a, 12b), having storage places for load in rack levels situated one above the other, and a load manipulation unit (4; 4'; 4"), comprising at least one first load-lifting device (34a; 84a) with a liftable and lowerable transport device (36a; 86a) for storing and retrieving load as well as a first buffer device (35a; 85a) with provisioning devices (43, 44) for temporarily storing one or more pieces of load, and at least one rack aisle (15; 15.1, 15.2) extending between adjacent storage racks (12a, 12b) and along the load-lifting device (34a; 84a) as well as the first buffer device (35a; 85a), and guide tracks running in at least some of the rack levels along the rack aisle (15; 15.1, 15.2), and one or more autonomous conveyor vehicles, which are displaceable along the guide tracks, for transporting the load between the storage places of the storage racks (12a, 12b) and the provisioning devices (43, 44) of the load manipulation unit (4; 4'; 4"; 4'"), and a conveying system (54a, 55a; 69, 71) connected to the load-lifting device (34a; 84a) for transporting load to and from the load-lifting device (34a; 84a), wherein the conveying system comprises a first conveying device (54a; 69) for transporting load to the load-lifting device (34a; 84a) and a second conveying device (55a; 71) for transporting load from the load-lifting device (34a; 84a), wherein the first and the second conveying device (54a; 69; 55a; 71) are located opposite to each other, and wherein in at least some of the rack levels, the buffer device (35a; 85a) comprises a fixed first buffer path section and fixed second buffer path section, in which the provisioning devices (43, 44) are arranged, and wherein the load-lifting device (34a; 84a) is arranged between the buffer path sections (41a, 42a) and the conveying devices (54a, 55a; 69, 71) in such a way that the transport device (36a; 86a) for storing and retrieving load can be vertically positioned relative to the rack levels either between two oppositely situated provisioning devices (43, 44) or between the conveying devices (54a, 55a; 69, 71), so that a load may either be conveyed between the transport device (36a; 86a) and one of the provisioning devices (43, 44) or between the transport device (36a; 86a) and one of the conveying devices (54a, 55a; 69, 71), characterised in that in those rack levels, in which the provisioning devices (43, 44) are arranged, the guide tracks extend continuously along the rack aisle (15; 15.1, 15.2) and the load-lifting device (34a; 84a) as well as the provisioning devices (43, 44), and the first buffer path section with the provisioning devices and the second buffer path section with the provisioning devices as well as the load-lifting device (34a; 84a), which is arranged between the conveying devices (54a, 55a; 69, 71) and the buffer path sections (41a, 42a) and has the liftable and lowerable transport device (36a; 86a) for storing and retrieving load, are provided sideways next to the rack aisle (15; 15.1, 15.2) along the guide tracks so that in the respective rack level, either the provisioning device in the first buffer path section or the provisioning device in the second buffer path section can be approached by the conveyor vehicle via the guide tracks for retrieving and storing load and that the provisioning devices of the first buffer path section each form a removing path for the load in all the rack levels, in which they are arranged, and the provisioning devices of the second buffer path section each form a storing path for the load in all the rack levels, in which they are arranged.