QoSFM: QoS Support for Metadata I/O in Parallel File Systems

Large parallel file systems (PFSs) must service multiple independent workloads concurrently. Workloads often require different quality of service (QoS) of metadata I/O. However, existing PFSs are unable to differentiate metadata I/O from different workloads. There are many researches on QoS support of storage system, they do not focus on metadata I/O of PFSs as one metadata I/O can have several sub-operations and different sub-operations have different access size. In addition, users cannot specify metadata QoS requirements without a suitable QoS specification. This paper presents a novel scheme QoSFM (QoS Support for Metadata) to support metadata I/O QoS in PFSs. QoSFM allows users to specify workloads´ metadata QoS requirements through our two-layered QoS specification mechanism. QoSFM can dynamically translate the workload-level goals into system resource needs such as service time per time window and sub-operation latency. Client-side controllers throttle the metadata I/O based on service time allocation to meet the throughput goal while metadata servers (MDSs) reorder the sub-operations based on deadlines to meet the latency goal. Extensive simulations show that QoSFM can effectively satisfy workload-level metadata I/O QoS requirements. Meanwhile, results also show that QoSFM has low overhead.