Design Choices for Utilizing Disk Idleness in a Virtual Machine Environment

In virtualized environments, an operating system may not have complete knowledge about its resources, as it sees only virtualized forms of physical resources. The Virtual Machine Monitor which has access to the physical resources, however, is not aware of the abstractions of the operating system. In this paper, we discuss how this lack of information can hinder the implementation of certain mechanisms that require both kinds of information. Specifically, we address how information about disk idleness can be passed to virtual machines so that idle disk periods can be effectively utilized to maximize disk bandwidth. The main focus of this paper is the discussion of various mechanisms that could be applicable in a virtualized environment in order to effectively expose such information and exercise control. We discuss designs to infer the number of dirty pages in each domain from the VMM, and to coerce a domain to flush its dirty pages. Finally, we present an evaluation of our approaches.