Storage SLA Guarantee with Novel SSD I/O Scheduler in Virtualized Data Centers

Service level agreements (SLAs) for storage performance in virtualized systems are difficult to guarantee, because different consolidated virtual machines have their own performance requirements. Moreover, hard disk drives (HDDs) in virtualized systems are being replaced by solid-state drives (SSDs). SSDs have higher throughput and lower latency than HDDs; however, they pose new challenges in terms of SLAs. In this paper, we determine that existing I/O schedulers working with SSDs fail to guarantee SLAs among virtualmachines, and do not effectively utilize the high performance of SSDs. To address this issue, we propose the opportunistic I/O scheduler (OIOS), a novel I/O scheduler for SSDs. OIOS guarantees SLAs and fully utilizes the high performance of SSDs. To support realistic SLAs, OIOS provides diverse SLA support functions, including reservations, limitations, and proportional sharing. In addition, OIOS accepts SLAs that are specified in four measurement types: bandwidth, I/Os per second (IOPS), latency, and utilization. Experimental results show that OIOS increases the aggregated bandwidth of VMs by 80 percent compared to mClock, while achieving a similar level of fairness. In addition, we evaluate the proposed scheduler with realistic benchmarks, such as Filebench and the Yahoo CloudServing Benchmark. OIOS successfully guarantees the requirements of diverse SLAs with different metrics.