Although most people still think of WORM (Write Once Read Many) as a form of optical disk storage, tape WORM is an increasingly popular option. In light of new compliance concerns, tape-based WORM can be an inexpensive alternative tooptical WORMs, especially in cases where the data needs to be accessed infrequently.
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Optical WORM drives can't be rewritten because of the physical characteristics of the optical disk system, especially the media. Magnetic tapes, of course, can be rewritten. Tape WORM systems use a combination of software and hardware techniques to make the tapes both non-rewritable and non-erasable. A more recent wrinkle is disk-based WORM which uses the same sorts of techniques to similarly protect files on hard disks.
The issue that is stimulating interest in all kinds of WORMs is compliance. While most of the spate of new laws regarding electronic records retention doesn't require WORM storage, some, notably the Securities and Exchange Commission's Rule 17a-4, do specify non-rewritable and non-erasable media. Because the SEC rules are more specific and stricter than most, they have become the default standard in many companies.
As a result of the new interest, a number of companies are offering non-optical WORM products. They include Sony with a version of its AIT tape, IBM with TotalStorage Data Retention 450 and EMC with its Centera family.
As usual with storage, each class of products has different price-performance points. Tape WORM's biggest selling point is price. The systems, from such vendors as SpectraLogic are cheaper in terms of gigabyte stored than either optical WORM or WORM disk. The tradeoff is that access to the data is much slower. Optical WORM is a good deal faster than WORM tape, but it is also more expensive. WORM disk is the most expensive and by far the fastest recovery time. WORM disk is usually combined with another WORM alternative to provide long-term storage of the data.
How much of a problem access time actually is depends on how often the records are likely to be accessed. Generally records covered by compliance laws will be accessed infrequently, if at all, during their lifetime.
Optical WORM comes out relatively poorly in the price-performance measurements because the current optical technologies are somewhat under-sized for the volumes of data associated with compliance. Sony's PDD optical disk system, for example, holds a relatively parsimonious 11 GB per side on each disk. However optical storage manufacturers are working diligently to increase capacities. Sony is reportedly promising to double PDD capacity by 2005 and double it again to 43 GB per side by 2007.About the author
Rick Cook has been writing about mass storage since the days when the term meant an 80K floppy disk. The computers he learned on used ferrite cores and magnetic drums. For the last twenty years he has been a freelance writer specializing in storage and other computer issues.