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In classical machine virtualization, a hypervisor runs multiple operating systems simultaneously, each on its own virtual machine. In nested virtualization, a hypervi-sor can run multiple other hypervisors with their associated virtual machines. As operating systems gain hyper-visor functionality—Microsoft Windows 7 already runs Windows XP in a virtual(More)
Multilevel caching, common in many storage configurations , introduces new challenges to traditional cache management: data must be kept in the appropriate cache and replication avoided across the various cache levels. Some existing solutions focus on avoiding replication across the levels of the hierarchy, working well without information about temporal(More)
Virtual machine (VM) time travel enables reverting a virtual machine's state, both transient and persistent, to past points in time. This capability can be used to improve virtual machine availability, to enable forensics on past VM states, and to recover from operator errors. We present an approach to virtual machine time travel which combines Continuous(More)
We have implemented a virtual machine (VM) for Java which executes on a cluster. Our cluster VM completely hides the cluster from the application, presenting a single system image (SSI) (i.e., the application sees a traditional virtual machine). At the same time it leverages the cluster to achieve improved performance for a range of applications. We show(More)
<i>Digital Preservation</i> deals with ensuring that digital data stored today can be read <i>and interpreted</i> tens or hundreds of years from now. At the heart of any solution to the preservation problem lies a storage component. This paper characterizes the requirements for such a component, defines its desirable properties and presents the need for(More)