Virtualization provides many improvements over traditional hardware-based deployments. Of them all, few have had the same level of impact as high availability. Server-class computer systems commonly have built-in redundancy thanks to multiple CPUs, network cards, power supplies, and storage components. They can operate for years without interruptive failure. However, not all hardware components allow for redundancy, and multiple failures in a redundant configuration can accumulate to system failure. Even when fully functional, all that hardware redundancy holds up a single operating system (OS) kernel. If enough hardware fails or that kernel crashes, it ceases providing its services and may lose data. Even without problems, patching frequently requires reboots. Any outage deprives application access to users, leaving them unable to aid customers, damaging your organization’s reputation and revenue.