The Longevity of Optical Storage Media

When CD technology first came out it was reported as being indestructible and a permanent solution for storage. With passage of time ,as with all new technologies, there has been an interaction of sales hyperbole and physical reality. CD technology, when it first arrived at an affordable level, was capable of storing 650MB of data when conventional desktop computers typically had drives of 20 to 60MB capacity. Existing hard drive capacities have now well exceeded this technology. Similarly for DVD technology the same has now occurred and hard drive capacities are starting to even outstrip emergent BluRay technology. Optical media, however, is one of the best solutions currently available for long term archival storage for digital forensics.

delaminatedCDOne of the common problems with this form of technology is the ability to accurately estimate the longevity of the media. The layers that are used for the recording of the data on optical media are subject to the perils of oxidation in the same way as magnetic tapes.

A current industry norm is that it takes five years for CD or DVD media to start to deteriorate, delaminate, rot, or give trouble. This figure has reemerged at various times since the discovery of the issues related to the deterioration of the recording layers. This issue is a series one and there are now published standards for estimating the longevity of CD media (ISO 18921 and 18927). It should be noted, however, that these are simply models for estimating the longevity of the media. If you lose one bit of data in a digital recording of a song the impacts are relatively minor, but for digital forensics a one data bit change can invalidate the hashing checksums and make the evidence invalid.

Consistent in the literature relating to this issue of optical media longevity is that the quality of the physical media production on one of the major determining factors. It is therefore important when purchasing media for use in the optical drives for archiving that the best quality media be sought for use in the process. The other critical factor is adequate environmental control to reduce temperature change, eliminate humidity, and reduce exposure to UV light. The optimal temperatures and humidity levels are the same as for conventional IT equipment. The reduction in the levels of UV light can be achieved by simply making sure that the optical media is stored away from sources of direct UV light and preferably stored in a wrapping or receptacle that eliminates light. The current wisdom is that the CD or DVD of good quality can be relied on for 20 to 50 years if stored properly.

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