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  Preservation Procedure Policy: Define Bit preservation levels
Related Guidance Policy
Bit preservation
Definition/ Description The PREMIS definition of “preservation levels” is “Information indicating the decision or policy on the set of preservation functions to be applied to an object and the context in whicht the decision or policy was made.” (chapter 1.3)
The organization might differentiate between different levels of bit preservation, depending on various criteria.
A criterion could be based on the distinction of whether it concerns digitized material:  preservation copies and/or access copies, or digital born material. For example for the digital born national deposit material, higher levels might be required compared to digitized material of which the analogue version is also preserved. Digital objects preserved for access might require a different bit preservation level than preservation copies, for example because access copies need to be presented faster and often are created in a lower resolution than a preservation copy.
Another criterion in defining bit preservation levels might be the value of the digital objects to the collection. If the digital material is absolutely unique and irretrievable from anywhere else in the world in case of loss or errors a high level of bit preservation (e.g. four copies in very distant places with a high frequency of integrity check etc.) would be preferable.
Why In order to ensure the optimal storage capacity and safety level over time it is vital to be aware of the bit preservation level(s) in the repository.
Risks Unawareness of bit preservation levels may endanger the digital material as the repository may run out of storage capacity or underestimate the need for safety for specific collections.
Life cycle stage Preservation Planning
Stakeholder
Management:  defining bit preservation could be a policy act
Depositor:  needs to know that bit preservation and safety measures are performed properly
Regulator: concerned with the safety measures in bit preservation
Cross Reference Functional preservation
Examples The Royal Library, Denmark: ”For every collection there must also be a decision with regard to level of preservation, including i.a. bit preservation and encrypting.” Source: http://www.kb.dk/export/sites/kb_dk/da/kb/downloadfiler/PreservationPolicyDigitalMaterials_21092012.pdf
Control Policy Defining a formal bit preservation level, as for example NDSA have done (see below), will generate an appropriate set of control level policies to implement that level of preservation.  So taking Level 1 and Level 3 as examples:
Level 1
  • Number of copies of the data = 2
  • Location of copies MUST be in different locations/buildings
  • File checksum algorithm should be run on ingest
  • File checksum algorithm MUST be <value>
  • File format SHOULD be Open Source
  • File format SHOULD be able to be identifiedLevel 3
  • Number of copies of the data >= 3
  • Location of copies MUST be different
  • Location risk for location 1 MUST be different to Location risk for location 2 or location 3
  • File checksum algorithm should be run on ingest
  • File checksum algorithm MUST be <value>
  • Filechecksum-recalculation date <= today – 2 years
  • File format SHOULD be Open Source
  • File format SHOULD be able to be identified
  • File format MUST be widely used
Questions to foster discussions
  • Has your repository defined  bit preservation levels for the various parts of the collection?
  • Does your organisation know what needs different collections/parts of the collection have?
  • Has your organisation clearly estimated the value of the collection?
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