Checkpoint/restart of virtual machines based on Xen

System level virtualization provides several advan-tages: (i) customization is eased since virtual machines may be based on different systems; (ii) virtual ma-chines are isolated from hardware, subsequently appli-cations are isolated via the virtual machines; (iii) basic fault tolerance mechanisms – pro-active fault tolerance through virtual machine migration and virtual machine snapshot/restore; and (iv) basic load balancing mech-anisms – the capability to move and stop virtual ma-chines running in the system. However, the current Xen implementation does not natively provide mecha-nisms for virtual machine checkpoint/restart. This document presents the design of a reactive fault tolerant system, based on a checkpoint/restart mecha-nism for Xen virtual machines. We present the in-frastructure for the management of virtual machines’ checkpoint data as well as challenges for the implemen-tation of a virtual machine checkpoint/restart mecha-nism based on Xen.