In order to provide a greater level of preservation assurance to its customers, the University of California Curation Center (UC3) has upgraded the Merritt curation repository with a new version of the Fixity micro-service. “Fixity” refers to a method of verifying the bit-level integrity of digital content through the use of message digest numbers created by an algorithm that represent that file uniquely (or checksums). Every piece of content in Merritt receives an initial digest value as the result of the successful processing of the Ingest micro-service. (This is either a validated digest supplied by the content submitter or a digest newly computed by the Ingest service itself.) Once established, these values are then continuously recalculated and verified by the Fixity service. If any bit-level corruption is uncovered, the damaged asset can be replaced with a verified copy from a Merritt replication site. (In addition to the primary copy hosted in the University of California Office of the President (UCOP) data center, all Merritt content is automatically replicated to the UC Berkeley data center. UC3 is currently investigating options for a third replica, possibly hosted in cloud storage.) Work is now underway to expose the fixity status of managed content in the Merritt User Interface (UI) at the collection, object, version, and file level to provide collection managers and curators with summary view of content “health”.
The new Fixity service is able to perform its function with significant increases in performance and function over its predecessor. Among the new features are support for wide range of digest algorithms –each exhibiting a particular trade-off between cryptographic security and computational efficiency; flexible reporting (although currently restricted to UC3 administrative systems and users); and the ability to validate content outside of Merritt as long as it is addressable with a stable URL. The technical specification for the new service is available at <http://www.cdlib.org/services/uc3/curation/fixity.html>.
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