Data archiving systems rely on replication to preserve information. In
this paper, we discuss how a network of autonomous archiving sites can
trade data to achieve the most reliable replication. A series of binary
trades between sites produces a peer to peer archiving network. We examine
two trading algorithms, one based on trading collections (even if they are
different sizes) and another based on trading equal sized blocks of space
(which can then store collections.) We introduce the concept of deeds,
which track the sites that own space at other sites. We then discuss
policies for tuning these algorithms to provide the highest reliability,
for example by changing the order in which sites are contacted and offered
trades.  Finally, we present simulation results that reveal which policies
are most reliable.