DPack: Disk scheduler for highly consolidated cloud

Virtualization allows us to consolidate multiple servers onto a single physical machine, saving infrastructure cost. Yet, consolidation can lead to performance degradation, jeopardizing Service Level Agreement (SLA). In this paper, we analyze and identify the factors to the performance degradation due to consolidation - that is the wait time and the ready time. The wait time is the queuing time caused by other virtual machines (VMs). The ready time is the time the resource takes to be ready to service, such as the seek time incurred in traditional storage. The ready time can substantially deteriorate the request response time. Unfortunately, existing schedulers can only manage the wait time, but not the ready time. To control both quantities, we propose an adaptive disk scheduler called DPack. DPack schedules the VMs based on the likelihood of the VM failing the SLAs. DPack then adjusts the exclusive access time based on the VM resource access prediction. DPack considers the workload changes and request arrival to enhance robustness. We develop DPack based on the default disk scheduler in KVM and evaluate it against several existing disk schedulers available in KVM and Xen. The results show that DPack can improve the 99th percentile response time up to 76%. In the highly consolidated environment, DPack can also satisfy all the SLAs, while the other schedulers cannot meet the SLAs for at least 50% of the VMs.