There are many large archive libraries of reel to reel magnetic tape and tape cartridges, some several decades old and emanating from many different industries and applications. Some of these libraries are held in non climate controlled warehouses comprising of rack upon rack of unprotected tapes. The applications range from geophysical data obtained from the early 1970's on ships surveying underneath the sea bed for oil reserves, through to voice logging of transactions and verbal communications on telephone lines within the financial service industries. The explosion in growth of call centers during recent years has also expanded the digital logging of voice data exponentially.
These libraries of legacy tapes have been maintained on the basis that at some time in the future they may be needed. Also in some instances there is a legal requirement for their existence. Although the tapes have been archived the means to read the tapes has often been lost. If these tapes have not been stored in climate controlled conditions over time they will deteriorate due to temperature and humidity variations.
Typical tape failure due to aging often is layer to layer adhesion where the magnetic oxide layer attaches to the polyester backing of the next layer causing it to be torn off leaving a clear blank area where the magnetic layer once existed. This not only will result in the data on the magnetic layer removed to be lost, but also the tape will probably attach itself to part of the tape path within the drive and snap the tape.
In order to reduce the likelihood of this occurring the tape cartridges can be cycled through a well defined heat and humidity process for several hours or days. This climatic cycling not only reduces the likelihood of layer to layer adhesion but also reduces the instance of other physical characteristics including stress and brittleness within the magnetic coating and polyester base layer. This brittleness may cause excess read errors and again inhibit the successful reading of the tape.
Once a tape has failed, normally for physical reasons including snapping of the tape, most people conclude that the data on the tape is lost forever. This is not necessarily the case and there are many techniques to recover most of the data on the tape.
There are many archived libraries of tape cartridges used for voice logging within the financial services industry which were produced to monitor the telephone conversations of operatives undertaking financial transactions. Often these tapes must be maintained for legal reasons and may cover several decades of conversations.
In one such high profile case the magnetic tape in a critical DDS data cartridge snapped due to 'layer adhesion' within the magnetic coating causing the tape to adhere to to the read drive capstans and snap. Data Recovery Specialists was requested to retrieve the data on this tape. The data was written with Racal Wordnet 2 format, and it was possible to physically splice back the tape and read non damaged portions of data. This procedure allowed the engineers to rebuild the lost data by monitoring the extended check sums and error correction codes written at the time the original data was laid down. This is a laborious procedure and requires extensive knowledge of tape formats to rebuild the lost data byte by byte. As the format used low level correction codes all of the data on the tape cartridge was recovered by restoring the lost data from these codes.
The recovered data on this tape cartridge was the subject of criminal proceedings and allowed the lawyers to build a successful legal defence.