Recently, the exchange of data has increased with progress in information technology. The capacity of for storing data is also increasing. However, even if the capacity of global storage becomes extremely large, the capacity of local storage is always limited. Moreover, storage of files larger then the available local storage is impossible. This paper discusses use of a network to construct a cheap, high trust and PB class, decentralized storage system using many hundreds of PCs in an educational environment. The performance of this 'large-scale virtual disk' is investigated both during normal operation and in instances of failure.