## 1 Introduction  
Determining the amount of stock in the supply chain is one of the optimization problems in the area of logistics (trade-off situation). If the number of warehouses is reduced, the inventory level may be, with the same service level (measured by the availability of inventory for customers), lower than in a larger distribution network. Although in decentralized distribution, warehouses are located close to customers, the failure to adjust the level of inventories to the actual demand may result in a shortage of goods stored in them. This means that it is possible to offer the same or even a higher level of logistics customer service and reduce the costs of maintaining inventories in one central warehouse. The costs of maintaining inventories are related both to the level of inventories in terms of quantity and their value: costs of money which is frozen in stocks, loans, losses due to their maintenance, theft, etc. As for storage costs, they are mainly related to the amount of stored goods and their storage susceptibility. When using warehousing services,warehousing costs can be related to the level of inventory in a comparable way to the cost of maintaining the inventory. However, a company offering warehousing services may offer discounts to large customers. It can also offer a fixed rate for renting warehouse space. In addition, for more expensive goods and goods difficult to store, there may be a need to provide appropriate storage conditions. In the case of these costs, the parameters of the loads (weight, volume) as well as the method of packaging and the loading units used (e.g., pallets) are also important. In the case of an owned warehouse, the cost structure will be different than in the case of warehouse services; fixed costs (independent of the stock level) will have the largest share. However, the degree of the utilization of storage space is important, especially if, due to centralization, its use will be more efficient than in a decentralized network. The efficiency of the warehouse operation depends to a great extent on the organization of the storage and the technologies used both for storing and moving loads in the warehouse (e.g., combustion or electric trucks). The solutions used in warehouses, on the other hand, have an impact on the costs as well as on the level of logistics service, because the efficiency of the warehouse processes also affects the time to fulfil customer orders. To some extent, it may also affect the efficiency of transport processes by reducing the waiting time of transport means for loading. Moreover, there will be fewer manipulations in the case of a central warehouse (reloading, moving inside a warehouse) than in the case of a network of warehouses. The efficiency of the logistics processes depends on the distance at which deliveries are made. However, this impact is not clear-cut, taking into consideration that in the case of centralization strategy, a given company may decide to use a more efficient transport solution (transport and handling technology, faster transport, e.g., air). It depends also on the form of ownership of transport: owned or a hired and whether a company cooperates with transport companies, forwarding companies, or specialized logistics operators who are able to deliver small loads frequently, quickly and on time, using their own distribution network e.g. with the use of cross docking. Due to the reduction of the number of warehouses, not only the internal costs of these deliveries may be higher, but also the external costs of transport. However, this impact is not unequivocal for similar reasons to those mentioned above. The increase of the efficiency of transport processes in the case of the centralization strategy (e.g., thanks to the cooperation with logistics operators) may also contribute to lowering the external costs of transport.