The CLOCKSS Archive: Long-Term Preservation for Scholarly Content

By Craig Van Dyck, Executive Director, CLOCKSS

January 2018

Just before the December holidays, the CLOCKSS Archive “triggered” 21 journals for open access. These were 21 of the journals that SAGE Publishing had acquired from Libertas Academica; SAGE had decided to cease publishing them, and to cease providing access. That’s when CLOCKSS stepped in, to preserve users’ access.

CLOCKSSCLOCKSS is a “dark archive” of scholarly content. With 30 million journal articles and 65,000 books, and growing rapidly, CLOCKSS is a leading preservation service for libraries and publishers who want to be sure that scholarly content will continue to be available to end-users for the long-term, no matter what might happen with the accessibility of the content.

Governance by the Community

CLOCKSS is a free-standing 501(c)(3) non-profit charitable organization. Its Board of Directors includes 12 libraries and 12 publishers, who together discuss issues and make policy ( CLOCKSS is 11 years old, and is financially stable and sustainable.


CLOCKSS uses the award-winning preservation technology, LOCKSS (Lots of Copies Keep Stuff Safe), that was developed by and is maintained by the Stanford University Library. The C in CLOCKSS stands for Controlled. CLOCKSS has all its content replicated on 12 servers, at leading academic libraries around the world ( The core of LOCKSS’s preservation capabilities is a polling-and-repair mechanism, by which mutually-distrusting peer systems continuously validate the integrity of the data they hold in common. In this way, though the contents of the archive are “dark”, we can maintain a high degree of confidence that the bits themselves are healthy over time, and that the original content can be made available intact in the case of a trigger event. CLOCKSS was certified as a Trusted Repository by the Center for Research Libraries in 2014 ( and is the only certified repository with a perfect score for Technologies, Technical Infrastructure, and Security. CLOCKSS believes that our technology is the most robust long-term preservation solution.

Global Network of Servers

The CLOCKSS servers are located at 12 leading academic libraries around the world, including Australia, Hong Kong, Japan, Germany, Italy, the UK, Canada, and the US (


If content that is being preserved in the CLOCKSS Archive has disappeared from the web – or is in danger of disappearing – then CLOCKSS will “trigger” the content for open access. In its 11 years, CLOCKSS has triggered 53 journals comprising 14,000 articles, which is a very small percentage of the 2000+ journals and 30 million articles in the Archive ( CLOCKSS is committed to providing Open Access to triggered content.

2018 Priorities

In the near-term, the top priorities for CLOCKSS are:

  • Complete the 3-year project to upgrade our global network of servers.
  • Continue the LOCKSS software re-architecture, making it more modular, with the modules usable by more parties; and bringing in more open source components.
  • Reach out more to libraries to articulate the CLOCKSS value proposition.
  • Continue adding the complete journal backfiles of the largest publishers.
  • Add more books.
  • Review the CLOCKSS scope, to ensure that all key elements of scholarly publishing are being preserved, e.g. metadata, and “supplementary material”. For example, as of late 2017 we are adding Code Ocean, a software repository, to our archive.

Library Support and Publisher Participation

Libraries make voluntary contributions to CLOCKSS, in recognition of libraries’ responsibility as stewards of the scholarly literature on behalf of their faculty and students. Publishers sign an agreement with CLOCKSS, which defines rights, responsibilities, and fees. The library support levels and publisher fees are posted on the CLOCKSS website ( There are 300 library supporters and 250 publisher participants.

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