How should images be backed up?

Copying to CD might be useful for short term backups but that on its own it isn't a very sustainable *long-term* preservation strategy. The reason for this is that the dyes used by recordable CDs (CD-R) tend to break down over time.

For more information, see section: 1.1.6 in Ross and Gow (1999). The same authors wrote in their executive summary that they felt that the stability of CD-R was over-rated and "far from being a secure medium it is unstable and prone to degradation under all but the best storage conditions." Best practice would beto keep an additional copy on some magnetic media. For more details see: Ross, S., Gow, A., 1999, Digital archaeology: rescuing neglected and damaged data resources. London: South Bank University, Library Information Technology Centre, February.

In practice, preservation is about managing information content over time. It is not enough just to make backups, but to create (at the time of digitisation) well-documented digital master files. Copies of these files should be stored on more than one media type, and (ideally) in more than one geographical location. These files should be used to derive other files used for user access (which may be in different formats) and would be the versions used for later format migration or for the repackaging of information content. If the files are images, the 'master' file format should be uncompressed, e.g. something like TIFF.

This is not to denigrate making backups in any way. Any service will need to generate these to facilitate its recovery in the case of disaster.

Creating a full 'digital master' with associated metadata will be a complex (and therefore expensive) task that should be done once only and at the time that the resource is being digitised. All equipment needs (or the choice of a digitisation bureau) should be considered with the creation of such digital masters in mind.

Projects will also need to decide where these digital masters should be kept for the duration of the project itself and where backup copies of them (and maybe other parts of the service) should be stored. Thought could be given to subscribing to a third-party storage service. An example is the National Data Repository at the University of London Computer Center (ULCC).

The various service providers of the Arts and Humanities Data Service (AHDS) will also provide a long-term storage service for digital resources. They have also published various guides to good practice.

Further Information