Capture Your Collections: Small museum version
Evaluating media

Several factors must be considered when planning for image file storage:

  • Cost may be the most important criterion in selecting the storage devices and media. It will be important to budget for both initial and ongoing costs.
  • Storage capacity is also an important criterion. The benchmark process will have defined the file size to be used and the total storage requirements can be calculated from this figure.
  • Access speed of the device may be an important criterion depending on how the images are to be used. If online access to master images is required, the appropriate storage device must be considered. The transfer and write speeds for the master images must also be considered for archival devices. The following are three configurations:
    1. Online access, required for immediate access of images, is usually provided through a network from a file server (networked hard disk). The image files must be available online; speed of access and file size are the main considerations.
    2. Semi-online access can be provided where the images can be accessed within a minute or two. This access can be provided from optical formats such as CD-ROM in a mechanical device such as a jukebox.
    3. Offline access requires the medium, such as CD-ROMs or tape, to be manually retrieved from storage and loaded.
  • Security of the images should be considered to prevent unauthorized access to images.

Data preservation

Protecting the integrity of a digital image must be a top priority for any digital preservation strategy. Preservation of images is an example of the ways in which content, defined in terms of structure and format, poses integrity problems for digital archives. It is difficult to plan a migration strategy, as it can be very difficult to anticipate the needs for migration, how much formatting will be required, and how much the process will cost. The process of migration can degrade data quality and this fact has implications for the integrity of the data.

Storage conditions

Storage conditions are an important factor in the preservation of certain types of storage media. Cooler and dryer storage conditions will extend life expectancy. Recommended conditions are a temperature between 10 and 20 degrees Centigrade and a relative humidity between 20 and 50 percent.

Magnetic tape is the least stable medium owing to its inherent instability, which leads to chemical deterioration and physical wear from use. Optical disks can become unreadable because of warpage, corrosion or cracking in the reflective layer, and from dye deterioration or delamination.

The dangers of obsolescence

With technologies rapidly changing, electronic media are constantly becoming unreadable as new media and devices emerge and as the old disappear. Therefore data must be transferred to new media types and formats, as necessary. The purpose of migration is to preserve the integrity of digital objects and to retain the ability to retrieve, display and otherwise use.

Records should be migrated to new media and/or formats before the current format deteriorate or become obsolete. Both periodic inspections of storage media to identify any deterioration and continuing review of the evolution of the technology for signs of obsolescence are needed to determine when to migrate records.

This should be done for several reasons:

  • Refreshing relates to preservation of the media; it is simply copying digital files from one storage device to another of the same type. Files should be migrated to new media before the current media deteriorate.
  • Migration relates to the upgrade of the media to preserve the integrity of digital files and to retain the ability to retrieve them in the face of constantly changing technology. Files should be migrated to new media formats as the latter become viable and before current media become obsolete.
  • Transformation relates to the translation of the current file formats to new file formats as they become viable. This may happens as a new standard becomes available or when current software become obsolete. If the files are in a proprietary format, problems may arise, as changes to the specifications of the file format may have been implemented by the format owner. In such cases, difficulty may be experienced when accessing the files.