Ask almost any systems administrator about libraries, and you will likely get a discourse on currently available tape technology, the corresponding cartridge robustness, and suitability for robotic tape handling. After a deep breath, the SA you queried might continue with a one-sided discussion of software for backup and archive management. Somewhere in the midst of this education, you might break in with, OK, but what about alternatives to tape? Ah, yes. The alternatives, the SA responds in his or her best W.C. Fields imitation.
If the assumption is traditional backup operations, our hypothetical SA's response would be natural. No other form of media has had any success in replacing tape for normal data backup purposes. Various tape formats and capacities are available for different types of environments. Some tape formats are best suited for individual workstation backup, while others lend themselves to the more stringent requirements of larger tape libraries connected to servers, networks, or Storage Area Networks (SANs). There are over a dozen common tape formats for archiving data in various ways.
With so many choices available, why would you want to seek additional alternatives? Perhaps because your intended backup purpose is non-traditional, and thus potentially falls outside the range of conventional backup procedures. Non-standard requirements often call for the examination of alternative solutions. And, it was in that spirit that we asked vendors of non-tape libraries for information about their products.
Even before CD-ROMs became ubiquitous, various vendors were offering CD-ROM servers, and CD-ROM jukeboxes, in which quantities of CD-ROMs could be made broadly available to users on the network. Such devices served the purpose of providing access to pre-recorded data, such as system documentation, on a system-wide scale. But, the concept of a library usually entails being able to write to the device directly, so CD-ROM devices, while useful, hardly qualified as libraries.
Once advances in CD recording technology brought drive prices within reason, CD-Recordable (CD-R) libraries of moderate capacity were brought to market. CD-R offers write-once, read-many capability, similar to that of some types of magneto-optical (MO) drives, but at a lower cost. Before any dust could settle on the discs, however, CD-reWriteable (CD/RW) drives became available and took their place alongside CD-R as a viable library alternative. CD/RW has the same capacity (about 650 MB/disc) as CD-R, and is only slightly more expensive than the earlier devices and media.
Although MO drives actually pre-dated commonly available CD-R, the cost factor of both the MO drives and the higher capacity media tended to keep MO in a narrower market segment. Low-end MO drives were popular with graphics professionals, among others, who needed moderately high capacity (100 MB-plus) and greater reliability than then-existing competing products. (Remember, this was before Iomega introduced Zip and Jaz drives.) Higher capacity MO drives and media carried even higher prices, and thus, tended to be used in more specialized applications, where the additional cost could be justified.
The hot disc technology (non-magnetic), of course, is DVD. Originally named Digital Video Disc, until the engineers realized that digital video was data, the technology is now more frequently referred to as Digital Versatile Disc, or simply DVD. DVD media is similar to CDs in size, but can hold far more data, depending on the recording scheme used. As is common with most disc-related technologies, read-only versions came out first. The original driving force behind DVD was, of course, high-quality movies -- better quality than even SuperVHS, and far more convenient. However, with movies as the mass-market force behind DVD, there is an associated copy-protection problem for the film industry. That fact, among others, is hampering the development of the technology to some extent.
Unfortunately, the data side of DVD, which is of the most interest to us, has fallen into multiple camps (can you say VHS and Beta in the same breath?), notwithstanding the existence of an industry group, the DVD Forum. DVD-R was the first to market, when Pioneer introduced a DVD-R drive following the 1.0 specification for about $17,000 in late 1997. DVD-RAM, the specification for which was developed within the DVD Forum, followed in the summer of 1998, and drives are now manufactured by Hitachi, Matsushita/Panasonic, and Toshiba, with retail prices now at less than $600 for single units. Currently available DVD-RAM libraries use drives from these manufacturers. However, Hewlett-Packard, Philips, and Sony broke ranks with the other members of the DVD Forum, and introduced a competing specification for DVD+RW. DVD+RW drives may be available by the time you read this, and libraries supporting these drives are sure to follow. DVD-RAM drives use caddy or cartridge-enclosed discs, and hold 2.6 GB per disc. In contrast, the DVD+RW discs will hold 3 GB and will not require a caddy. Links to various manufacturer sites are included in the FAQs listed in the resource list at the end of this article.
Manufacturers of DVD libraries appear to be allowing the mass-market side of the industry call the design shots. Although DVD discs can be double-sided, none of the drive manufacturers are discussing delivery of double-sided drives. The thought, apparently, is that PC users of single drives will be willing to manually flip the disc, rather than paying a premium for a double-sided drive. Library manufacturers seem to be happy with mass-market prices for drives and will likely provide disc flippers as part of the library robotics, when necessary.
When to Slip a Disc
Although CD-R, CD/RW, and DVD libraries can serve as general-purpose backup devices, media prices and overall capacity of tape libraries still present a compelling argument for conventional methods. Where our so-called alternative libraries can make sense, however, is in applications where the nature of the media provides greater convenience, or as near-line storage, perhaps in a hierarchical storage management scheme. Consider, too, the stability of the data. CD-R, for example, being a write-once format, provides a level of data permanence not offered by erasable media. DVD-R has the same feature, but is still too expensive for general use at most sites. Sites with particularly stringent requirements, however, may find DVD-R cost-justifiable, especially with DVD-R version 2.0, and the substantially reduced drive cost (around $5,000). Potential applications for DVD-RAM, and other DVD formats, include multimedia, medical-imaging applications, digital prepress, and Internet/intranet databases.
When considering specifications, some of the CD terminology carries forward, some not. When specifying capacities, for example, manufacturers equate one billion bytes with 1 GB, rather than the 230 measure used elsewhere. Transfer rates (read and write) for DVD-RAM drives are about 1350 KB/sec, or about the same as an 8x CD-ROM's read speed. Although HP has announced a DVD+RW drive, with a capacity of 3 GB and a speed of 1.25x (1700 KB/sec), these drives are not yet generally available, either as standalone, or in libraries.
It is unclear which of the DVD rewriteable formats will eventually dominate the market. DVD-RAM and DVD+RW are likely front-runners, with significant manufacturers on both sides. In many cases, however, that question may be moot. CD-R, CD/RW, and DVD-based libraries are likely to be point solutions for a specific set of requirements. In such cases, upgrade paths may be less important than other decision factors.
The accompanying table of products includes specifications from vendors who responded to our inquiries. Other vendors whofailed to respond may have products in this category as well.
Useful DVD Resources
DVD for Data Storage FAQ (maintained by Steve Rothman, includes pointers to other resources, vendors, and Linux info):
General DVD FAQ (maintained by Jim Taylor):
The DVD Forum (industry group):
372 Turquoise Street
Milpitas, CA 95035
Fax: (408) 934-7007
Globalstor Data Corporation
9960 Canoga Ave, Unit D9
Chatsworth, CA 91311
Fax: (818) 701-7756
6840 Indiana Ave, Suite 130
Riverside, CA 92506
Fax: (909) 781-4105
3342 Gateway Blvd.
Fremont, CA 94538
Fax: (510) 353-1845
140 Technology Dr, Suite 500
Irvine, CA 92663
Fax: (949) 789-3150
9625 W. 76th Street
Eden Prairie, MN 55344
SONY Electronics Inc.
3300 Zanker Road
San Jose, CA 95134
Fax: (888) 322-5275