We present a disk array organization that adapts itself to successive disk failures. When all disks are operational, all data are replicated on two disks. Whenever a disk fails, the array reorganizes itself, by selecting a disk containing redundant data and replacing these data by their exclusive or (XOR) with the other copy of the data contained on the disk that failed. This will protect the array against any single disk failure until the failed disk gets replaced and the array can revert to its original condition. Hence data will remain protected against the successive failures of up to one half of the original number of disks, provided that no critical disk failure happens while the array is reorganizing itself. As a result, our scheme achieves the same access times as a replicated organization under normal operational conditions while having a much lower likelihood of loosing data under abnormal conditions. In addition it tolerates much longer repair times than static disk arrays/

Provisioning a storage system requires balancing the costs of the solution with the benefits that the solution will provide. Previous provisioning approaches have started with a fixed set of requirements and the goal of automatically finding minimum cost solutions to meet them. Such approaches neglect the cost-benefit analysis of the purchasing decision. Purchasing a storage system involves an extensive set of trade-offs between metrics such as purchase cost, performance, reliability, availability, power, etc. Increases in one metric have consequences for others, and failing to account for these trade-offs can lead to a poor return on the storage investment. Using a collection of storage acquisition and provisioning scenarios, we show that utility functions enable this cost-benefit structure to be conveyed to an automated provisioning tool, enabling the tool to make appropriate trade-offs between different system metrics including performance, data protection, and purchase cost.