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after migration. The redirection of communications must also take into
account of optimized group communications, in addition to point-to-point
communications. Existing VM technologies are inadequate to address these
challenges. Current virtualization technologies embed the coni guration
and management information within the VM image. The coni guration
information, therefore, cannot be easily changed to accommodate resource
l uctuations, or be managed automatically. Users need to perform coni g-
uration and to set up the execution environment manually. VM creation,
deployment, and migration are currently achieved via copying the VM
image. This approach is very slow, problematic, and does not support adap-
tation. None of the existing systems supports communication direction and
redirection [10]. These four challenges are largely unsolved with current vir-
tualization technologies. We introduce cutting edge research in the rest of
the chapter to address these challenges.
16.2 Recent Work in Virtual Machines for Grids
Some efforts in virtualization techniques focus on virtualization on a set
of given computing [2,3,11-15] or communication [16,17] resources. These
techniques, including VM and VN, emulate computing resources on top
of a given physical computing infrastructure and form the basis of the
virtualization technology. Since in these studies the virtual resources are
bound to their underlying physical resources, these techniques do not
address the issues of coni guration description and dynamic coni gura-
tion of virtual computing environments.
Several projects endeavor to enable virtualization in distributed comput-
ing environments. Figueiredo, Dinda, and Fortes explored the feasibility of
virtual machines on grid computing and proposed a VM-based architec-
ture for grid computing [18,19]. They aim to isolate the user and admin-
istrator's views, provide system security, and ease the administration. A
virtual private workspace [5] focuses on the authentication, authorization,
and resource management of a virtual environment in the grid. However,
these projects are designed to use current virtualization technologies in a
distributed environment, not to extend current virtualization technolo-
gies for system coni guration management. They do not support the mod-
eling, incarnation, and migration of a virtual environment, and cannot
address the coni guration and maintenance challenges.
Researchers from Stanford have performed some experiments on VM
portability [20]. Other works include Internet Suspension and Resume
[21] and Xen Checkpointing and Resume [3]. As their names suggest, they
suspend or checkpoint a VM on one computer and resume it on another.
Because a system-level VM has a huge image, it cannot be migrated
directly in a timely manner. Even though migration performances are
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