1. A system comprising: plural virtualization systems configured in a cluster; storage accessible to each virtualization system of the cluster, wherein each virtual machine operative in a virtualization system of the cluster includes virtualized memory and virtualized storage device, and wherein for each virtual machine operative in the virtualization system of the cluster, the storage maintains a representation of virtual machine state that includes at least a description of a hardware system virtualized, including a description of a type of processor in the hardware system virtualized, and an image of virtualized memory state for the virtual machine in addition to the virtualized storage device, and wherein the image of virtualized memory state for each virtual machine in the cluster is encoded in a different volume of the storage so that no volume of the storage includes images of virtualized memory state for multiple virtual machines; a failover system that, responsive to an interruption of, or on, a particular one of the virtualization systems, transitions at least one affected virtual machine to another virtualization system of the cluster and resumes computations of the transitioned virtual machine based on state encoded by a corresponding one of the virtual machine states represented in the storage; and encapsulations, in the respective different volumes of the storage, of the virtual machine state for respective ones of the virtual machines, wherein each of the encapsulations encodes at least the description of the hardware system virtualized and backing state date of its corresponding virtual machine, wherein each of the respective encapsulations further encodes one or more snapshots of virtual machine state and one or more virtual disks for a particular virtual machine of the cluster, and wherein each of the respective encapsulations is configured to limit guest access to data residing in the one or more virtual disks.