The Oxford Common File Layout
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The Oxford Common File Layout (OCFL) is an emerging data standard that describes an application-independent approach to the storage of digital information in a structured, transparent and predictable manner. With the most recent release, v1.1, OCFL implementations are becoming increasingly popular within institutions looking for long-term preservation solutions that are robust against corruption, offer storage diversity and are easily transportable between storage vendors, thus protecting their content into the foreseeable future. In this presentation we will discuss the specific design goals and methodologies involved in developing and maintaining the OCFL specification as well as explore different ways institutions are implementing OCFL as part of their digital preservation programs. Implementers will speak about their use case requirements for their individual institutions and reasoning behind selecting OCFL as well as discuss their desired outcomes.
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The Oxford Common File Layout
- 1. SLIDESMANIA. The Oxford Common File Layout Understanding the specification, institutional use cases & implementations Arran Griffith - Fedora Program Manager Stefano Cossu - Harvard University Libraries Thomas Wrobel - Oxford University, Bodleian Libraries
- 2. SLIDESMANIA. The Oxford Common File Layout (OCFL) “A simple, non- proprietary, specified, open-standards approach to the layout of preservation persistence.” ● Purpose: provide a preservation-centric, common approach to filesystem layout for digital repositories ● Developed and maintained by the OCFL Editorial Board ● Several implementations of the specification are in active use
- 3. SLIDESMANIA. Benefits of the OCFL Parsability Storage Diversity Robustness ● Readable by both humans and machines Versioning ● Checksums to protect against corruption and errors between storage technologies Completeness ● Ensures content can be stored on any type of infrastructure including conventional systems or cloud systems ● So the repository can be rebuilt from the files it stores ● All changes are versioned, allowed a repository’s history to persist
- 5. SLIDESMANIA. OCFL for Digital Preservation in ● OCFL was incorporated to enhanced long-term digital preservation for Fedora repositories ● Fedora 6.x writes all data to OCFL formatting using the OCFL-java library ○ Purpose of this was to take advantage of the transparency offered by the OCFL file structure Benefits: ● Application-independent persistence ● Human and machine readable data ● Ability to rebuild repository from contents on disk ● Fewer migrations in the future Standards = What to do Fedora + OCFL = How to do it
- 7. SLIDESMANIA. DRS at a glance Scale Long-standing legacy Migration time & costs DRS Futures project ➜ 3-year capital-funded project to replace current DRS ➜ Design a new repository without migrating data ➜ >10M objects, >100M files, 2Pb replicated ➜ Exponential growth foreseen in the future ➜ More than 1 year to migrate from POSIX to OCFL ➜ Don’t want to do that again ➜ In operation and continuously maintained for 22 years ➜ In need of a complete re-engineering
- 8. SLIDESMANIA. Value of OCFL for DRS Approach What OCFL provides Assumptions Challenges ➜ A file layout standard specifically designed for long-term preservation ➜ A software-agnostic data layer ➜ A community dedicated to resolving digital preservation problems ➜ How do we guarantee performance? ➜ What about backward compatibility? ➜ Do we have enough OCFL-compatible software choices? ➜ A standard adopted by a sufficiently large & diverse community that guarantees the promised stability ➜ A healthy community of implementers and service providers to implement & maintain the required tools ➜ Maintain a “storage fabric” separated from the application layer ➜ Replace current DRS without migrating or rearranging the data layer
- 10. SLIDESMANIA. University of Oxford - Bodleian Libraries ● 300,000+ works ● 100,000 of these have public binary files of which ORA holds the only digital copy ● Works include: ○ Articles, conference papers, theses, research data, working papers, posters, and more… Digital Preservation Microservices (DPMS) Oxford University Research Archive (ORA) Digital Preservation Service Purpose: preserve a versioned copy of a digital object which will allow the DPMS to monitor, analyse and support the system Purpose: monitor and support the preservation of binary content and metadata
- 11. SLIDESMANIA. Advantages of OCFL Advantages of Fedora University of Oxford - Bodleian Libraries ● Platform & application agnostic ● DPS OCFL layer decreases migrations ● Back-up & monitoring more simplified ● Parsability ● Single parent directory = no need for index or management application to analyse a given object ● Well documented RESTful API ● Transaction management ● Authentication & Authorization ● Community support and continued engagement
- 12. SLIDESMANIA. What’s Next… University of Oxford - Bodleian Libraries ● Performance and scale testing of Fedora 6.x + OCFL ● Export ORA repository into DPS and integrate with day-to-day operations ● Expand to other services with the Bodleian Libraries Reach Us: Thomas Wrobel - thomas.wrobel@bodleian.ox.ac.uk ORA Team - ora-dev@bodleian.ox.ac.uk
- 13. SLIDESMANIA. Resourc es The Oxford Common File Layout www.ocfl.io Fedora Program Info Wiki: https://wiki.lyrasis.org/display/FF/Fedora+Repository+Home Documentation: https://wiki.lyrasis.org/display/FEDORA6x Get Connected: https://wiki.lyrasis.org/display/FF/Mailing+Lists+etc Harvard DRS Futures https://sites.harvard.edu/drs-futures/
- 14. SLIDESMANIA. Thank You Arran Griffith - arran.griffith@lyrasis.org Stefano Cossu - stefano_cossu@harvard.edu Thomas Wrobel - thomas.wrobel@bodleian.ox.ac.uk
Editor's Notes
- Hello My name is Arran Griffith and I am the program manager for the Fedora Program. I am joined today in-person my my colleague Stefano Cusso from Harvard University Libraries. Our other co-presenter, Thomas Wroble, sends his regards that he wasn’t able to make it, but he’s given us some info on the work they are doing at the Bodleian to share with you. But Stefano and I are talking generally about the Oxford Common File Layout specification, and sharing how each of us are incorporating the OFCL as components of our systems to take advantage of what the specification offers.
- The Oxford Common File Layout (OCFL) is a specification that describes an application-independent approach to the storage of digital information in a structured, transparent, and predictable manner. It was developed to provide a standardized approach to filesystem layout within a digital repository that would also promote preservation and support long-term object management best practices within the repositories. It is defined and developed by and editorial board who is responsible for the upkeep, continued development and maintenance of the spec. Currently there are several implementations of the OCFL in active use around the globe - all of which can be found on the ocfl website - ocfl.io. Today though, we are here to share with you our individual use cases involving the OCFL and talk about why we’ve opted to use it and how we’re doing that. If you have any questions about the OCFL specifically, Stefano and I are more than happy to try to answer them, but we are by no means the OCFL experts so we will defer to them and encourage you to join the #ocfl chanel on the Code4Lib slack or reach out on the website which I’ve linked too at the end.
- As I mentioned, the purpose of OCFL is to provide an application-indenpendent approach to storing digital content. The specification dictates the way files are structured and written and this, in terms of digital preservation offers many benefits. These are the 5 main benefits offered by the specification: The first being parsability - this means that the files themselves, once written to OCFL are done so in a simple, plain text format which is readable to both machines and humans which means they can be understood in the absence of the original software. Next is robustness. OCFL provides checksums for both the content and metadata to ensure robustness against errors and data corruption between storage technologies. OCLF also offers native versioning - This is part of it’s core DNA. It uses a forward delta algorithm which eliminates unnecessary duplication between versions. Built into the specification is the principle of immutable versioning. Everything is there and exists as versions to allow their history to persist. As I mentioned before, by nature, OCFL allows for storage Diversity - you can use any type of storage system you’d like because the simple file system metaphor with it’s basic files and directories allows you to operate on disk or in the cloud. And lastly OCFL offers Completeness. And what this means is that everything is preserved in the structure of the spec including all the data and associated provenance which allows you to theoretically rebuild your repository from the files you have. Should the unspeakable ever happen and the hardware fails, you can simply take your oclf repo and stand it up again elsewhere because it would be complete and preserved as such.
- As you can see there is a lot to gain from implementing the OCFL specification. Now we are going to share a little bit about why each of our programs and institutions hs chosen to incorporate this standard into our systems and software.
- Fedora is here to represent how we, as a software, are taking advantage of OCFL and incorporating it into our core. We use the OCFL-java implementation of the spec and this was the major feature improvement with Fedora 6. The community made the decision to use the OCFL standard within the persistence layer of Fedora in order to give our users back the transparency they were looking for and were used too from Fedora 3. OCFL replaced the MODESHAPE back end of Fedora 4, which was kind of this black box of unknown territory. Making the decision to do this required a major re-write of the core software but now gives us this very transparent and largely enhanced long-term digital preservation tool by offering Fedora 6 + OCFL. Fedora benefits from using OCFL for preservation for several reasons: Fedora itself provides a means of reading, writing and delivering digital files to your users, and OCFL provides the standard for which those files are preserved. If we consider long-term preservation, if Fedora were to ever go away, you have all the info within OCFL to stand up your repository again simply from the files on disk. The metadata is still intact as well as all of the provenance required to meet preservation standards. And because of the standardized way that OCFL dictates the file system layout, migrations should be more simplified going forward. There should be no need to reformat data in any way to move into newer versions of the software as was the case with previous Fedora migrations. OCFL and Fedora provides preservation that is also independent of the storage medium. This gives Fedora users more options for storing their objects. Since OCFL stores plain files, you can use whatever storage medium you choose, whether that be local storage or cloud storage. There is support within Fedora via the java client for cloud storage So to sum it all up - standards equal WHAT to do, and this combination of FEdora and OCFL provide the HOW. It’s the combination of the two that provide the best possible software solution for long-term digital preservation.
- General info about LTS and DRS
- Mention downsides of the approach: restricted choice of solutions that conform to OCFL