Guidelines for the use of CDs and DVDs as storage media in preservation repositories

CDs and DVDs are a rather unreliable recording media, and therefore one may assume that they should be considered as unfit for digital preservation, especially in a long term preservation environment. However, due to their very low cost and widespread distribution, they have been widely used, and in many cases are still used as storage media in preservation repositories, by several organizations, including very respectable ones. It is quite unlikely that these organizations may be convinced to give up the use of optical removable disks as storage media, at least in the short and medium term. Therefore, some serious action needs to be taken to keep the situation under control. This paper moves in this direction, and contributes to the problem by proposing a methodology to analyze the reliability of these devices, and a set of operational guidelines that, by means of appropriate controls and procedures, may guarantee reliability levels that could be considered appropriate even in a long term digital preservation environment. These guidelines are a good example of how, using an adequate redundancy and an accurate monitoring scheme, a reliable system, a storage system in this specific case, could be built out of unreliable components.