A storage system comprising: first and second storage sections (12, 14), each configured for storing containers arranged in multiple rows (Z1-Zn) at various horizontal levels with respect to ground, and a first group of transportation devices (A1, A2, A3) configured for moving in a horizontal direction along corresponding pairs of rails arranged at multiple horizontal levels in a passage between the first storage section and the second storage section so as to have access to the containers arranged in both the first and second storage sections, wherein the first group of transportation devices (A1, A2, A3) includes a first transportation device (100, A1) movable along a first pair of rails, and a second transportation device (100, A2) movable along a second pair of rails arranged above the first pair of rails, wherein the first transportation device (100, A1) is configured to access containers arranged in the first and second storage sections at a first set of rows, and the second transportation device (100, A2) is configured to access containers arranged in the first and second storage sections at a second set of rows provided above the rows of the first set, and wherein each transportation device is movable along a corresponding pair of rails, whereby each transportation device is configured to include a container access mechanism movable up with respect to the corresponding pair of rails so as to handle one or more containers stored in a row above the corresponding pair of rails, and movable down with respect to the corresponding pair of rails so as to handle one or more containers stored in a row below the corresponding pair of rails, characterised in that the first set and the second set include a pre-determined number of rows common to the both first and second sets, the number of common rows is less than the number of rows in the first set and the number of rows in the second set. first and second storage sections (12, 14), each configured for storing containers arranged in multiple rows (Z1-Zn) at various horizontal levels with respect to ground, and a first group of transportation devices (A1, A2, A3) configured for moving in a horizontal direction along corresponding pairs of rails arranged at multiple horizontal levels in a passage between the first storage section and the second storage section so as to have access to the containers arranged in both the first and second storage sections, wherein the first group of transportation devices (A1, A2, A3) includes a first transportation device (100, A1) movable along a first pair of rails, and a second transportation device (100, A2) movable along a second pair of rails arranged above the first pair of rails, wherein the first transportation device (100, A1) is configured to access containers arranged in the first and second storage sections at a first set of rows, and the second transportation device (100, A2) is configured to access containers arranged in the first and second storage sections at a second set of rows provided above the rows of the first set, and wherein each transportation device is movable along a corresponding pair of rails, whereby each transportation device is configured to include a container access mechanism movable up with respect to the corresponding pair of rails so as to handle one or more containers stored in a row above the corresponding pair of rails, and movable down with respect to the corresponding pair of rails so as to handle one or more containers stored in a row below the corresponding pair of rails, characterised in that the first set and the second set include a pre-determined number of rows common to the both first and second sets, the number of common rows is less than the number of rows in the first set and the number of rows in the second set.