1. A system comprising: plural virtualization systems configured in a cluster; storage accessible to each virtualization system of the cluster, wherein for each virtual machine operative in a virtualization system of the cluster, the storage maintains a representation of virtual machine state; encapsulations, in respective volumes of the storage, of virtual machine state for respective ones of the virtual machines, wherein each of the encapsulations encodes at least one or more virtual disks for a particular virtual machine of the cluster, wherein each of the respective encapsulations is configured to limit guest access to data residing in the one or more virtual disks; and a failover system that transitions at least one virtual machine affected by an interruption to another virtualization system of the cluster.