Maximizing Throughput in Replicated Disk Striping of Variable Bit-Rate Streams

In a system offering on-demand real-time streaming of media files, data striping across an array of disks can improve load balancing, allowing higher disk utilization and increased system throughput. However, it can also cause complete service disruption in the case of a disk failure. Reliability can be improved by adding data redundancy and reserving extra disk bandwidth during normal operation. In this paper, we are interested in providing fault-tolerance for media servers that support variable bit-rate encoding formats. Higher compression efficiency with respect to constant bit-rate encoding can significantly reduce per-user resource requirements, at the cost of increased resource management complexity. For the first time, the interaction between storage system fault-tolerance and variable bit-rate streaming with deterministic QoS guarantees is investigated. We implement into a prototype server and experimentally evaluate, using detailed simulated disk models, alternative data replication techniques and disk bandwidth reservation schemes. We show that with the minimum reservation scheme introduced here, single disk failures can be tolerated at a cost of less than 20% reduced throughput during normal operation, even for a disk array of moderate size. We also examine the benefit from load balancing techniques proposed for traditional storage systems and find only limited improvement in the measured through-