University Secretary

Do not keep data that you cannot afford to lose on portable media. The life-span of a CD or DVD is determined by several factors, including its manufacturing quality, its handling, and environmental conditions. If it is of low quality or is subjected to careless handling or high levels of humidity and heat, it may last only a couple of years and, in some cases, no more than a number of months.

To help to preserve any data that you choose to store on disks, you should take the following precautions:

• Keep disks away from direct sunlight;

• Do not leave them in drives unnecessarily;

• Store them upright in protective cases to guard against dust and environmental changes, and reduce the risk of gradual bending;

• Always hold disks by the outer edge or centre to avoid marking the surface with fingerprints or scratches and affecting their readability;

• Use disks that only record once, so that the data cannot be changed or overwritten. Rewriting reduces the life-expectancy: the more erase-recording cycles to which a disk has been exposed, the shorter its life-span will be.

• Make at least two copies of each disk and store them in separate and secure locations;

• Check the readability of the data periodically and refresh it (i.e. copy the data onto a new disk) every few years.

It is possible to purchase higher quality CDs and DVDs known as 'archival gold'.  These use a dye for the recording layer that is resistant to fading, while the reflective layer is made from gold to protect against corrosion; they also have a thick, protective coating and are better sealed to stop moisture from entering. Archival gold disks are expected to last for decades, provided they are handled carefully.

It is, however, always advisable to store critical data on the network, so that it will be protected by appropriate back up and disaster recovery procedures.