Using snow as a metaphor for the digital data we use to convey ideas, Tom Cramer, James L. Hilton, Sebastien Korner, and David Minor make the case for building a Digital Preservation Network (DPN) in an EDUCAUSE Review article. 

"Currently in its start-up phase, DPN is building a digital preservation backbone that connects five existing (or soon to exist, in the case of APTrust) preservation-oriented repositories: the Academic Preservation Trust (APTrust), Chronopolis, HathiTrust, Stanford Digital Repository (SDR), and the University of Texas Digital Repository (UTDR)... By linking the repositories and developing frameworks around audit, transport, and intellectual property management, DPN will make it possible to create "dark" copies (i.e., no end-user access) of the content across the various nodes while maintaining high confidence in the integrity and retrievability of that content."