Hierarchical RAID: Organization, Operation, Reliability and Performance
The authors consider two level Hierarchical RAID (HRAID) arrays with erasure coding at both levels. The main advantage of HRAID is tolerating disk array controller failures in addition to disk failures, so that it is suitable for storage clouds based on bricks. They consider an HRAID with N nodes consisting of independent RAID controllers and M disks per node. Each node tolerates the failure of l disks and the controllers use a software protocol to coordinate their activities to implement an inter-node RAID level tolerating k node failures.