On Disk I/O Scheduling in Virtual Machines

Disk I/O schedulers are an essential part of most modern operating systems, with objectives such as improving disk utilization, and achieving better application performance and performance isolation. Current scheduler designs for OSs are based heavily on assumptions made about the latency characteristics of the underlying disk technology like electromechanical disks, flash storage, etc. In virtualized environments though, with the virtual machine monitor sharing the underlying storage between multiple competing virtual machines, the disk service latency characteristics observed in the VMs turn out to be quite different from the traditionally assumed characteristics. This calls for a re-examination of the design of disk I/O schedulers for virtual machines. Recent work on disk I/O scheduling for virtualized environments has focused on inter-VM fairness and the improvement of overall disk throughput in the system. In this paper, we take a closer look at the impact of virtualization and shared disk usage in virtualized environments on the guest VM-level I/O scheduler, and its ability to continue to enforce isolation and fair utilization of the VM’s share of I/O resources among applications and application components deployed within the VM.