Various forms of both fully- and semi-automated order processing and fulfillment systems are known.  They, and the components they comprise, may take many forms.  As one example, U.S. Pat.  No.  2,701,065, describes handling and storing of goods stored in containers stacked in freestanding rows.  Another example is shown in EP 0767113 (Cimcorp™), where a mechanism for removing a plurality of stacked bins using a robotic load handler in the form of a rectangular tube which is lowered around bins and is able to grip a in at any level is described. 
A frame-structured system is described in WO 98/049075A wherein multiple bins are stacked by virtue of being retained in a grid frame structure.  Bins are handled by a moveable load handler, as described in Norwegian patent NO 317366, which is able to pick up the top bin from a stack guided by rails in a large grid.  In some implementations, multiple load handlers may be used to increase capacity and reduce access times. 
There is need, however, for improvement in the efficiency of systems and processes for storing and retrieving containers in such systems. 
Fully- and semi-automatic goods storage and retrieval systems, various aspects of which may sometimes be referred to as “order fulfillment,” “storage and retrieval,” and/or “order picking” systems, can be implemented in a wide variety of types and forms.  One manner of providing access to goods stored for fully- and/or semi-automatic retrieval, for example, comprises placement of goods, which may be of any desired type(s), in bins or other containers (hereinafter referred to generically as containers), and stacking and/or otherwise disposing the containers vertically in layers, and optionally in multiple columns and/or rows, such that individual containers may be accessible by wholly or partially-automated container retrieval systems.  Such systems can for example comprise various combinations of containers; container stack support mechanisms, which may include mechanical devices such as frames and/or free-standing, stackable, and/or otherwise specialized container(s); and automated or semi-automated (i.e., “robotic”) retrieval devices, such as load handlers which may for example operate on grids or other forms of rails, using wheels, and/or on other forms of mechanical traveling devices. 
For example, as shown in FIG.  2, goods storage and retrieval systems may be provided in forms comprising rows and columns of stacked containers, in combination with overhead rail-operated load handlers configured to access the containers for both storage and removal, from above, as shown in FIGS.  3 and 4A.
Automatic or semi-automatic order picking systems can include many processes which in some examples may be broadly separated into at least two main aspects.  One aspect involves the moving of containers with product into and out of storage with a mechanized or other system.  Another aspect involves the transfer of product into, out of and between containers, which may often involve a manual and/or automated process(es). 
Optimising container moving processes can, in some examples, involve managing conveyors, cranes, shuttles, robotic load handlers etc in a way which optimizes the throughput of the storage and retrieval system.  In a real industrial application, this may involve trade-offs between utilization and performance of different parts of the system, especially as contention for various resources occur over time. 
Optimising product moving processes (such as order picking and container replenishment) can, in some examples, focus on keeping the manual (e.g. human) and (semi-)automated pickers/mechanisms constantly engaged without waiting periods.  In a general merchandise or grocery picking operation, there may be variations in the time required to perform these tasks, depending on size, weight, shape, robustness etc.  of the individual products.  For example, during container replenishment, it may take 20 times longer to fill a container with one product than with another product. 
Providing a buffer between the container moving mechanical system and the product moving systems may, in some embodiments, reduce or eliminate the delays caused by waiting for a container, a device (such as a load handler, conveyor, etc.)  or another resource from the other system to become available.  In some examples, this may enable separate or overall optimization of the two systems. 
In some example embodiments, the use of buffer may improve labour utilization.  In some example scenarios, the productivity of a container replenishment (inbound) process may increase by 30-40%, and the order picking productivity may increase by 20-30% by the introduction of adequately sized buffers.  In some examples, the present disclosure provides methods and systems for arranging such buffers in a cost and space efficient manner. 
The productivity of the robotic load handlers in some example systems may also be increased by reducing the vertical movement of the load handlers at replenishment and order picking stations.  In some scenarios, this may allow more frequent access for the robotic load handlers to each dropoff and pickup location, which may enables a higher pick rate and/or higher labour productivity.  Some embodiments of the present disclosure may significantly reduce vertical movement for the load handler. 
In some example scenarios and/or embodiments, the efficiency of the above-described systems, and other types of storage and retrieval systems, may be improved by providing for the storage and access of containers, in stacks, from above and below, as shown for example in FIGS.  5-7, etc.