This paper studies the archival problem: how a digital library can
preserve electronic documents over long periods of time.  
We analyze how an archival repository can fail and we present different
strategies that help solve the problem. We introduce ArchSim, a simulation
tool that for evaluating an implementation of an archival repository
system and compare options such as different disk reliabilities, error
detection and correction algorithms, preventive maintenance, etc. We use
ArchSim to analyze a case study of an Archival Repository for Computer
Science Technical Reports.