Sys Admin's Desktop Tape Library Buyer's Guide
Ralph Barker Call it what you will - the flip side of the coin, the other dropped shoe, or Murphy's Law - computing certainly seems to have its share of corresponding gotchas when it comes to advances in technology. Such is particularly true with storage and backup technologies. So, while advances in disk technology have made it easier to provide users with the vast amounts of storage they need, we are still faced with the challenge of performing regular backups. However, such backups are now sized in the scores of gigabytes. And, although large, high-capacity tape libraries have long been the solution for enterprise-level storage, smaller, more local backup devices may be better for departmental application servers and many Web servers. These factors sparked our interest in tape libraries designed for desktop use, the topic of this buyer's guide. For this product survey, we set an upper limit of libraries having one or two drives and up to 16 slots for cartridge tapes. Additionally, qualifying products had to be designed for desktop use, and the tape technology used had to provide at least 10GB of uncompressed storage per tape. We have included key features in the accompanying specification table, but we can't include all details that might be of interest to you in your particular setting. Use the table to build a "short list" of products that appear to satisfy your requirements, and then request more detailed information from those vendors. Contact information is provided only for vendors who responded to our request for information. Other vendors may also have products that meet the requirements specified. Before delving into the feature table, however, a quick review of the available tape technologies may help you make your library choice. Which Tape? The current leading tape drives fall into four categories:
Note that all of these tape technologies use cartridges that lend themselves to robotic handling. Capacities (uncompressed) range from about 2GB for early 4mm DDS and 8mm formats to 35GB for the current top-end DLT-7000 drive. The most popular formats range between 12GB and 40GB, however. Table 1 shows the comparative capacities and transfer rates for presently available popular formats. Those with capacities of 10GB or more per tape (uncompressed), and which are worthy of current consideration in a library configuration are shown in bold. Although choosing the drive with the highest capacity per tape may seem to be the obvious choice, other factors come into play. For example, cost of both the drive and the media may be important factors to consider. While the DLT-7000 drive currently offers the highest capacity and the fastest transfer rate, the drives and media they use also tend to be the most expensive. Compatibility with your existing store of archival tapes may also be a factor to consider. Most of the formats will read tapes from at least one generation back, few have both read and write backward compatibility. The 4mm DDS-3 drives from Sony and Hewlett Packard and the MLR-series from Tandberg are good in this respect. Although backward compatibility is a major concern for single-drive installations, it is less so for libraries. It is unlikely that you will want to read older tapes created on single-drive systems on the library. Being able to restore a tape that was created in the library on a single-drive system is a more important consideration. Thus, choosing a drive technology that you can justify in a single-drive configuration may influence your overall choice. Duty Returns Almost all tape drive manufacturers provide data regarding the expected mean time between failure (MTBF) for their products. This information, although interesting, is of marginal use for single-drive installations and even less-telling in a library. Most single-drive tape configurations, for example, assume a duty cycle of less than 20%, meaning that the tape drive is actually operating less than 20% of the time. In a library, the duty cycle for the tape drive goes up considerably. Tape drives in large, enterprise-level libraries may be functioning almost constantly, backing up huge amounts of live data across a dedicated, high-speed interconnect. A tape drive in a desktop library probably will not operate at a full-time level, but it will still be higher than the usual 20% duty cycle expected for single drives. Thus, MTBF is of little real value for evaluating tape drives for your library. A more informative statistic is the manufacturer's field return rate. Although few manufacturers quote this statistic in their marketing materials, most will provide the information upon request. This statistic tells you the percentage of drives being returned to them for repair or replacement from customers in the field, and provides an excellent gauge of the drive's reliability in a library configuration. A field-return rate of around 5% is probably reasonable, but lower rates are even better. Balance this information against other considerations for the libraries on your "short list." Now and the Future Although DLT was the early darling of library manufacturers, other tape drive manufacturers have made advances in the capacity curve during the last couple of years. Exabyte, one of the first drive manufacturers to supply multi-gigabyte tape drives to the UNIX market, lost considerable market share to Quantum when that company resurrected the DLT technology from assets it purchased from Digital Equipment Corp. Exabyte's late-to-market Mammoth drive, however, has put the company back in the high-capacity race. Similarly, Tandberg Data has given new life to the QIC market with its MLR1 and the recently introduced MLR3 drives. Another relatively new entrant to the field that bears consideration is the 8mm AIT drive from Sony. Although still behind the DLT-7000 insofar as capacity and transfer rate, 8mm AIT competes well in the mid-range and has numerous appealing features. And finally, 4mm DDS drives got a shot in the arm from DDS-3 drives manufactured by Hewlett Packard and Sony. Although earlier versions of DDS drives were popular for single-drive backup solutions for UNIX workstations and small servers, few library manufacturers found them to be robust enough for the higher duty cycles of libraries. DDS-3 appears to have solved that problem. Virtually all of the tape drive manufacturers have announced road maps for their technologies for several product generations into the future. Such road maps provide a degree of comfort for those making current product-purchase decisions. In most cases, a current purchase only makes sense if the drive manufacturer can show viability for the product line into the future. Expect to see tape capacities in the 100GB-plus range for most of these technologies within the next few years. Another movement in the tape drive industry that bears watching is the Linear Tape-Open group formed by IBM, HP, and Seagate. These companies have announced the cooperative development of two new tape technologies, Accelis and Ultrium, aimed at the network server and open systems markets. Accelis is intended to provide fast access to data, and Ultrium is planned for high capacity. Accelis looks quite similar to IBM's Magstar MP tapes, and Ultrium appears to be aimed at head-on competition with the square, single-reel cartridge format of Quantum's DLT. Although no road map for actual product availability has been announced as we go to press, the partnership of these companies may add choices in the future.
Contact Information
ADIC
Breece Hill Technologies
Concorde Technologies Inc.
Digital Equipment Corp.
Exabyte Corp.
GigaTrend Inc.
Hewlett-Packard Co.
MediaLogic ADL Inc.*
Overland Data Inc.
Procom Technology, Inc.
Qualstar Corp.
Quantum*
Seagate Tape Operations
Spectra Logic Corp.
Storage Dimensions
Straightline
Tandberg Data Inc.
Transitional Technology Inc.
Western Scientific Inc
*Responded to questionnaire, but submitted products outside the scope of the survey.
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