The TPT-RAID Architecture for Box-Fault Tolerant Storage Systems

TPT-RAID is a multi-box RAID wherein each ECC group comprises at most one block from any given storage box, and can thus tolerate a box failure. It extends the idea of an out-of-band SAN controller into the RAID: data is sent directly between hosts and targets and among targets, and the RAID controller supervises ECC calculation by the targets. By preventing a communication bottleneck in the controller, excellent scalability is achieved while retaining the simplicity of centralized control. TPT-RAID, whose controller can be a software module within an out-of-band SAN controller, moreover conforms to a conventional switched network architecture, whereas an inband RAID controller would either constitute a communication bottleneck or would have to also be a full-fledged router. The design is validated in an InfiniBand-based prototype using iSCSI and iSER, and required changes to relevant protocols are introduced.