Time travel in the virtualized past: cheap fares and first class seats

“Time travel” in the storage system is accessing past storage system states. Legacy application programs could run transparently over the past states if the past states were virtualized in a form that makes them look like the current state. There are many levels in the storage system at which past state virtualization could occur. How do we choose? We think that past state virtualization should occur at a high storage system buffer manager level, such as database buffer manager. Everything above this level can run legacy programs. The system below can manage the mechanisms needed to implement the virtualization. This approach can be applied to any kind of storage system, ranging from traditional databases and file systems to the new generation of specialized storage managers such as Bigtable. Granted that time travel is a desirable feature, this position paper considers the design axis for virtualizing past states for time travel, and asks what amounts to the question, can we sit in first class and still have cheap fares?