NDSA 2021 Fixity Survey

Executive Summary

The digital preservation community has long recognized the importance of fixity information in enabling and facilitating digital preservation activities. In particular, fixity information is used to review digital content to ensure that its bit-level representation remains unchanged over time, thus proving that the content (and indeed the digital preservation processes that manage and maintain it) can be trusted. To enable greater understanding about how fixity information was employed in practice, in 2017 the NDSA carried out a survey to gather this information from the community. The 2017 Fixity Survey Report summarized the results of the survey and provided a valuable snapshot of community fixity practices. Understanding that digital preservation is an emerging discipline and practices evolve over time, it was anticipated that the 2017 Fixity Survey would not be a one-time exercise and that future surveys would create a longitudinal dataset to increase our understanding of this evolving field.

The NDSA Fixity Survey Working Group was re-established in 2021. Survey questions from 2017 were reviewed and new questions were added to cover additional areas of interest. To enable analysis of trends and evolving practices between the 2017 and 2021 surveys, a crosswalk was established. A total of 166 survey responses were recorded, of which 116 completed surveys were used for analysis. Several key points can be made from studying the survey results:

• The results demonstrate just how important fixity information is to the digital preservation community, with over 96% of survey respondents confirming that they utilize fixity information within their organization and over 98% of these using checksums (sometimes alongside other types of fixity information). The primary reason fixity information is used by the community is to determine whether data has been altered over time.
• Despite a clear consensus that the use of fixity information represents good practice, the results demonstrate huge variation in fixity practices across the community. There are a variety of practices reported across the survey questions, including at what point fixity information is verified, the frequency of checks, where fixity information is recorded, and the checksum algorithms in use.
• Variations in fixity practices within an organization are also common, with over 48% of respondents reporting that different fixity practices are employed for different content or media.
• The importance of recording and verifying fixity information is clear. Though nearly 27% of respondents never saw fixity checks fail, failures occasionally occurred for others and nearly 11% reported seeing fixity failures multiple times per year. Interrupted network transfers were reported as the most common reason for fixity failures.
• Receiving fixity information at the time of acquisition remains a challenge.
• Though fixity checking lends itself well to automation, for many it remains a fairly manual process, with a majority of respondents using manually-run software to carry out this activity

The Fixity Survey Working Group conducted follow-up interviews with some organizations to explore fixity practices in more detail. The resulting case studies, included within this report, provide a rich illustration of how fixity is used within specific organizations, and build on some of the findings of the survey itself.