Embodiments include systems and methods for providing throughput increase and/or physical expansion of a data storage library. Some embodiments include multiple robotic assemblies, each having its own hand assembly, which are electrically and mechanically integrated for concurrent use in a single storage library environment for increased throughput. Other embodiments include an active vertical pass-through assembly that operates to ferry cartridges from one storage library environment to another, vertically adjacent storage library environment. Some such embodiments use existing robotic mechanisms of the libraries to exploit a shared slot through which vertical pass-through functionality can be realized. Other embodiments include an active horizontal pass-through assembly that operates to ferry cartridges from one storage library environment to another, horizontally adjacent storage library environment. Some such embodiments include a separate robotic mechanism that couples with each library and actively passes a cartridge among them and is adjustable to varying spans between the libraries.