12. Digital archiving principles

Digital archiving has to observe the following core principles:

  • Each digital copy produced for archival purposes must be checked against the imported file ("verification"), be free of uncorrectable errors, and have the lowest possible number of correctable errors. An error status report has to be produced and kept for future monitoring. Digital recordings entering the archive from outside sources may, however, contain uncorrectable errors; again, an error status report including the position of such errors must be retained.
  • Each carrier containing digital recordings must be checked at regular intervals for data integrity.
  • Digital content must be copied to a new carrier whenever the number of errors increases significantly - at any rate before uncorrectable errors occur ("refreshment").
  • Digital content must be copied before the old carriers, formats, and/or hardware become obsolete ("migration").
  • It is essential to keep at least two digital preservation copies and to use additional copies for access as appropriate. The preservation copies should be kept in different locations whenever possible.

Whenever digital archiving is carried out, the core principles mentioned above must be observed. It is preferable that the checks should be performed automatically, as is possible with computer controlled equipment and automated equipment such as DMSSs (paragraph 13). If this is not possible, then manual checks will need to be undertaken on a statistically significant basis.

In their essence, these principles are identical with those recommended for the analogue world. A fundamental difference, however, is the qualitative dimension of the digital world, which permits objective validation of the integrity of recordings. Regular data integrity monitoring is amongst the core obligations of digital preservation routines. Digital carriers and systems may fail, without any warning, at any time. It is imperative, therefore, to have at least one duplicate (backup copy) of each digital archival copy, ideally in a separate place. Also, strategies for minimising risks to digital archives are greatly supported by digital technologies, specifically by networking between the primary collection, the user and backup archives.