Caching and migration for multilevel persistent object stores

We propose an architecture for scalable persistent object managers that provide access to large numbers of objects distributed over a variety of physical media. Our approach is lightweight in that we are interested in providing direct support for the creation, access, and updating of persistent objects, but only indirect support for the other functions traditionally associated with an object oriented database, such as transactions, back up, recovery, or a query language. This design allows application programmers access to the productivity and performance of using objects, while relying on an underlying hierarchical storage system to manage the large amounts of data. Our design is layered and multilevel in that it caches and migrates large-grained physical collections of objects called folios from tape to networked disks. Separately, it also caches and migrates smaller-grained physical collections of objects called segments between nodes on a network. Segments are then moved into memory as usual for persistent object managers. In this paper, we also describe the implementation of a system called PTool based upon this design and give a description of preliminary performance results.