The Keepers Registry currently has 8 participating archiving agencies:
- British Library
- CLOCKSS Archive
- Global LOCKSS Network
- HathiTrust
- Portico
- Archaeology Data Service
- National Science Library, Chinese Academy of Sciences
- e-Depot
A quick look at their descriptions suggests that some may be interested in archiving MathOverflow.
The Center for Research Libraries appears to be the main international entity for assessing and certifying the trustworthiness and reliability of major archiving agencies. Some reports can be found here.
I looked in more detail at Portico since it has a very nice description of its services. I think they would classify MathOverflow as an e-journal. Their aim is to provide digital preservation, not a backup system nor a redundant access point. So this service would be suitable for a separate read-only "e-journal" archive of MathOverflow content, not for a site mirror (even if read-only) nor for permanent storage of MathOverflow data dumps. Their publication agreement can be seen here and the terms look very reasonable to me. Their pricing model is also very reasonable: so long as MathOverflow does not make \$250k in revenues, our annual contribution would be \$250.
It appears that HathiTrust and e-Depot currently only accept "monolithic" documents such as books and cannot accept periodicals or similar objects. Archaeology Data Service only accepts documents relating to archaeology and history.
The Global LOCKSS Network has an interesting framework.
This section describes how a LOCKSS Box works. Specifically, a LOCKSS Box performs five main functions:
- It ingests content from target websites using a web crawler similar to those used by search engines.
- It preserves content by continually comparing the content it has collected with the same content collected by other LOCKSS Boxes, and repairing any differences.
- It delivers authoritative content to readers by acting as a web proxy, cache or via Metadata resolvers when the publisher’s website is not available.
- It provides management through a web interface that allows librarians to select new content for preservation, monitor the content being preserved and control access to the preserved content.
- It dynamically migrates content to new formats as needed for display.
The system seems rather flexible but I couldn't determine what content formats they could support in their archival units. To use that option, we would need to maintain our own archive (distributing content in a format that LOCKSS can support) and the participating libraries would each have a permanent and authoritative cache of our archive in their LOCKSS Box.
The CLOCKSS Archive has a basic mechanism similar to the Global LOCKSS Network but the goal is not to provide continued access to the resource like some of the above. Instead, CLOCKSS is designed to publicly release an archive only after a trigger event. The Title No Longer Offered event corresponds to the type of failure that Scott mentioned in the question.
I haven't yet found the relevant information for the British Library and the National Science Library of the Chinese Academy of Sciences.
From what I can tell so far, Portico, the Global LOCKSS Network and the CLOCKSS Archive all offer potentially useful services for the purpose of archiving MathOverflow. The Global LOCKSS Network appears to be the most flexible but it does not offer as much security as Portico and CLOCKSS. CLOCKSS offers fewer services than Portico, but combining CLOCKSS with the Global LOCKSS Network is a very competitive alternative to Portico.