LOCKSS: A Permanent Web Publishing and Access System

LOCKSS (Lots Of Copies Keep Stuff Safe) is a tool designed for libraries to use to ensure their community’s continued access to web-published scientific journals. LOCKSS allows libraries to take custody of the material to which they subscribe, in the same way they do for paper, and to preserve it. By preserving it they ensure that, for their community, links and searches continue to resolve to the published material even if it is no longer available from the publisher. Think of it as the digital equivalent of stacks where an authoritative copy of material is always available rather than the digital equivalent of an archive.
LOCKSS allows libraries to run web caches for specific journals. These caches collect content as it is published and are never flushed. They cooperate in a peer-to-peer network to detect and repair damaged or missing pages. The caches run on generic PC hardware using open-source software and require almost no skilled administration, making the cost of preserving a journal manageable.
LOCKSS is currently being tested at 40+ libraries worldwide with the support of 30+ publishers.

More here and here