Shadows is a research database system built at Helsinki University of Technology. Shadows has some interesting features, such as Copy-on-Write technology, snapshots, transparent raid, and performance which increases with load. My work was caching and some other bits. Couple of documents on the subject:

Tatu Yonen's Licensiate Thesis, probably best general description on technologies used in Shadows.

Heikki Suonsivu's Master's Thesis, about ELRU cache algorithm used in Shadows.