Scalability and Extensibility in the Denali Virtual Machine Monitor

March 30, 2005
Andrew Whitaker | University of Washington

Virtual machine monitors (VMMs) such as VMWare are useful for addressing a wide range of systems problems, including server partitioning, migration, intrusion detection, configuration debugging, and fault tolerance. Despite their broad applicability, the VMMs in common use today suffer from two deficiencies. First, traditional VMMs are not scalable: they do not support a large number of virtual machines on a single physical machine. This capability is essential for an emerging class of applications that require many, small protection domains. Second, traditional VMMs do not have a clean extensibility model. As a result, researchers have had to expend considerable effort to realize services such as migration and configuration debugging.

Our work on the Denali VMM has brought scalability and extensibility to the domain of virtual machine monitors. Along the way, we have reconsidered many of the fundamental VMM design decisions that were laid down by IBM’s pioneering work in the late 1960’s and early 1970’s. Denali achieves scalability using a technique called para-virtualization, which exposes a virtual architecture that differs from the underlying physical architecture. Denali achieves extensibility by cleanly exposing the implementation of virtual hardware devices such as disks and the Ethernet. This capability is sufficient to realize a broad class of services that introduce functionality below the virtual machine abstraction.

In the final part of the talk, I will discuss some of the services we have built on our extensibility platform. One such service is the Chronus tool, which helps to answer the age-old question: “Why has my computer stopped working?”

Speaker Details

Andrew Whitaker received B.S. degrees in computer science and math from Indiana University in 1999. After college, he enrolled in the graduate computer science program at the University of Washington. His primary area of interest is computer systems. Over the past several years, he has worked with Professor Steve Gribble on the Denali project, which has adapted virtual machine monitors to address challenges in such areas as security, reliability, and system administration. Andrew has also moonlighted as a networking researcher, under the tutelage of Professor David Wetherall. Andrew expects to graduate in August of 2005.