Checkpoint/Restart of Virtual Machines Based on Xen

System level virtualization provides several advantages: Customization is eased since virtual machines may be based on different systems; virtual machines are isolated from hardware, subsequently applications are isolated via the virtual machines; basic fault tolerance mechanisms - proactive fault tolerance through virtual machine migration and virtual machine snapshot/restore; and basic load balancing mechanisms - the capability to move and stop virtual machines running in the system. However, the current Xen implementation does not natively provide mechanisms for virtual machine checkpoint/restart.