The Dynamics of Storage Media

Selecting storage media may not at first appear to be a strategic decision, but racking and shelving in cutting-edge manufacturing and distribution centers do much more than idly store parts, work in process or finished goods.

Storage media — rack systems, pick modules, shelving and more — are fundamental components of inventory management. Depending on how it's used, a storage strategy can help or hinder the flow of material throughout a facility and beyond the four walls.

No single storage configuration works for every application. The right approach varies based on desired storage density, available floor space and building height, physical properties of the material to be stored, desired level of access to inventory and inventory rotation needs.

Selective vs. High Density

Stationary selective pallet rack is the most common and economical type of racking system. Selective rack's major claim to fame is 100% selectivity — every pallet is immediately accessible. In addition, it's easily assembled and reconfigurable.

However, a gain in selectivity can result in a loss of storage density, essentially, space utilization. Though access is ideal, selective storage requires a large amount of aisle space, which restricts the amount of material that can be stored in a facility.

However, there is a way around this problem. Selective rack can be modified through a double-deep configuration, a simple adaptation of 100% selective rack in which one row of rack is placed behind another. While selectivity is reduced, twice as many pallets can be stored, which can increase productive floor space by 60% to 65%.

Drawbacks of double-deep storage, however, include the need for specialized lift trucks to retrieve pallets in the rear position as well as the potential for honeycombing — when vacant space occurs after pallet loads are retrieved.

High-density storage systems take storage beyond selective rack, allowing an operation to store much more material in less space with fewer aisles. High-density systems can increase usable facility space by up to 75%. Although some inventory positions are not immediately available, these systems maximize space utilization, a significant advantage for applications in which facility space is costly to maintain, as with freezer and cooler operations. High-density systems also allow for fast-moving, high-volume order fulfillment.

There are many types of high-density storage systems, each having strengths and weaknesses. Drive-in and drive-through systems are generally considered the most economical high-density configurations. In a drive-in pallet rack, product is stored on continuous rails, and lift trucks enter one side of the rack structure to place or retrieve pallets. Drive-in racks normally store two to eight pallets per lane and are designed for frequent pallet movement.

Drive-in and double-deep storage both support last-in, first-out (LIFO) inventory rotation, meaning the last pallet placed is the first pallet retrieved. LIFO rotation is most often used for material that is not time-sensitive or perishable.

Operations handling food or other perishable material requiring the opposite material flow — first-in, first-out (FIFO) — may consider a drive-through rack system, in which lift trucks load from one side and unload from another, allowing FIFO rotation.