I am writing in response to the timely article on magnetic tape stiction by Norman Pascal in the November 1993 issue of the Recorder. Although most geophysicists prefer to ignore the unglamourous issue of tape storage, stiction of 9-track tapes is becoming a serious problem and must be addressed quickly.
Surveys recorded in the mid-eighties are most at risk. On one of our 1984 lines in North Sumatra, 50% of the data is nonrecoverable. The tape is literally transparent even though it has been stored in a cool, dry environment.
In 1992 Asamera began the process of archiving its 20,000 tapes to both 8 mm and ST-120 (VHS) media. This is the first such project in Indonesia and one of the first worldwide. Our experience may be of interest to other geophysicists.
Although the project appeared expensive, it was sold to management principally as a means to save money on long term tape storage. The cost of archiving our data is approximately equal to 5-7 years of tape storage. In addition it was promoted as a method of protecting the company's investment (by copying old and sticky tapes) and of insuring against lost of data (by archiving the original data onto two different media and storing these in two physically separate locations).
There are other benefits which a geophysicist would appreciate. One is the subsequent ease of reprocessing, tape copying and workstation loading. At a recent partners' meeting in Jakarta, we were asked for a copy of all the field tapes on a particular line. They flew home to Calgary the next morning with a single 8 mm cartridge. Our Tokyo partners requested 5000 km of migrated data from several different contracts. They had three 8 mm cartridges the following week. Our 8 mm cartridges are stored near the workstation allowing us to load or reload stack data within minutes.
Another by-product of the careful quality control required to do the archiving is the rediscovery of lost seismic lines. These lines are either absent from newer basemaps or else their field tapes are stored under an incorrect project or block name. To date we have restored three such lines to the basemaps. The archiving procedure restores order to tape listings rendered chaotic by decades of input and retrieval by clerical staff.
At a current rate of 1,000 tapes per mouth (including demultiplexing), our 20,000 tapes will be archived in just under two years. Final output will be approximately 150 8 mm cartridges (5 GB capacity) and 60 VHS cartridges (15 GB). Two full-time technicians are required in our office to check the tape listing, observer's notes, basemaps, film sections, operations. reports, processing reports, as well as the output QC listings and plots. Although we recommended destruction of the original tapes, the state oil company, Pertamina, insisted on continued storage of these tapes with costs charged to their own account.
The best method of archiving field tapes is to copy the various distinct surveys onto separate cartridges. Similarly, the simplest method of archiving stack tapes is to copy all the output tapes from each processing contract onto a separate cartridge for each contract. Each cartridge is accompanied by a listing of its contents. To locate a particular line, use a spreadsheet/database listing of the data on all cartridges in line number order.
The first question I am always asked is why did we choose to archive onto 8 mm and VHS media. The surprising answer is that the choice of media is not nearly so important as actually doing something. In several years time there will inevitably be new media, new drives, and new standards. It will be a simple matter to copy 60 VHS tapes onto the latest storage medium. By far the most difficult step is the initial procedure of copying 20,000 old, sticky, lost and disorganized tapes onto whatever medium one chooses.
Having said that, it is clear from Pascal's article that we chose the 8 mm cartridge because the drives are cheap and readily available. The VHS medium combines the benefits of inexpensive archival cost and reasonably-priced drives. It is important to use two output media in case one of them should deteriorate unexpectedly.
Archiving a huge unwieldy tape inventory is a formidable and unappetizing challenge. Unfortunately, it has to be done or else that data will be lost either to old age or stiction. It will eventually save you money. The benefits are clear. Better get after it.
Geoffrey T. Bennett
Senior Staff Geophysicist
Asamera Oil Indonesia
P.O. Box 2858, Jakarta, Indonesia