  Data storage systems are more reliable than their individual components. In
order to build highly reliable systems out of less reliable parts, systems
introduce redundancy. In replicated systems, objects are simply copied several
times with each copy residing on a different physical device. While such an
approach is simple and direct, more elaborate approaches such as erasure coding
can achieve equivalent levels of data protection while using less redundancy.
This report examines the trade-offs in cost and performance between replicated
and erasure encoded storage systems.
