Block shifting layout for efficient and robust large declustered storage systems

Modern disks are very large (SSDs, HDDs) and their capacities will certainly increase in the future. Storage systems use an important number of such devices to compose storage pools and fulfil the storage capacity demands. The result is a higher probability of a failure and a longer reconstruction duration. Consequently, the whole system is penalized as the response time is higher and a second failure will generate a data loss. In this paper, we propose a new method based on block shifting layout which increases the efficiency of a RAID declustered storage system and improves its robustness in both normal and failure modes. We define four mapping rules to reach these objectives. Conducted tests reveal that exploiting the coprime property between the number of devices and the block shifting factor leads to an optimal layout. It reduces significantly the redirection time proportionally to the number of disks, reaching 50% for 1000 disks and a negligeable memory cost as we avoid the use of a redirection table. It also allows the recovery of additional data in case of a second failure during the degraded mode which gives to our proposed method a huge interest for large storage systems comparing to other existing methods.