Does virtualization make disk scheduling passé?

We examine whether traditional disk I/O scheduling still provides benefits in a layered system consisting of virtualized operating systems and underlying virtual machine monitor. We demonstrate that choosing the appropriate scheduling algorithm in guest operating systems provides performance benefits, while scheduling in the virtual machine monitor has no measurable advantage. We propose future areas for investigation, including schedulers optimized for running in a virtual machine, for running in a virtual machine monitor, and layered schedulers optimizing both application level access and the underlying storage technology.