In this chapter, we talked about the types of system downtime and their impact and how to measure and increase the level of availability. One of the most important features, live migration, was also explained briefly. Finally, we went through the cluster filesystem in order to know how Proxmox maintains its configuration files. In the next chapter, we will talk about the key components that will be used when we build the cluster, including the DRDB device, reliable network, and a fencing device.