Digital Preservation Q&A - Recent questions tagged fixity

Is checking fixity at the folder level sufficient for knowing if any files within that folder that been altered?

Wed, 07 Feb 2018 11:37:59 +0000

Parity data for ISO images: anyone doing this? Best practices?

Wed, 25 May 2016 13:48:28 +0000

Earlier today I had a discussion with a colleague on possible ways to store (ISO) images of CD-ROMs and DVDs in our repository system. In addition to checksums, he suggested to also generate and store parity data for each image file (e.g. using the par2 tool: http://manpages.ubuntu.com/manpages/trusty/man1/par2.1.html). This would enable one to repair files in case of bit-level corruption.

This made me wonder how commonly parity info is used in digital archives, and if there are any best (or at least recommended) practices. E.g. what levels of redundancy are typically used? I'm not really familiar with this at all, and it's not a subject that is often mentioned in digital preservation discussions (but see https://twitter.com/anjacks0n/status/733281959762395139).

What tools do you use for the ongoing monitoring of checksums?

Tue, 09 Sep 2014 17:20:26 +0000

I am currently working on choosing and implementing a tool to continuously monitor checksums for our digital holdings (digitized content and born-digital materials) across our entire institution. We have a lot of data on our preservation server (we have many terabytes of data, and want to plan ahead for the near future when we break a petabyte) that we want to continuously monitor for bit-rot, and we're wondering about the experiences of other institutions.

What do you use to monitor the fixity of your preservation masters on an ongoing basis? What (generally speaking) is the workflow like to make sure that checksums happen as often as they're supposed to?

Bonus points if you know of a tool that is automated (or at least schedulable), and super-bonus points if it could work on our server and have multiple user accounts for different content administrators.

What are best practices/recommendations for how often to check fixity of content?

Thu, 24 Jul 2014 01:23:33 +0000

My institution is working toward incorporating fixed-interval fixity checks into our preservation workflow. I'm interested in hearing about what policies and procedures other institutions have implemented to manage this process and what your "fixed interval(s)" is/are. Context about the number of files you curate and how that has influenced your fixity check workflow would be extremely helpful.

Is simple fixity information valuable to digital stewards?

Wed, 23 Jul 2014 14:07:37 +0000

From #digpres14:

The BagIt specification includes an oxsum in the transfer materials. This oxsum is the size of the bitstream divided by the number of files. Why is simple fixity information like this included when each file also includes a checksum, a much more precise measure of fixity?

More generally, why do we care about this low-level fixity information?

To what extent do cryptographic hash (MD5, SHA1, etc.) collisions rates matter for fixity checking?

Mon, 03 Mar 2014 19:48:04 +0000

Given the probabilities of hash value collisions are MD5 hashes sufficient for ensuring file fixity? Or should SHA1 or SHA2 be used? Or, should folks be catching all three. I would be interested in both issues to consider for tamper resistance and for simply knowing if what I have is what I think I have.