There's a tape solution for every organization

Computer Technology Review, Nov, 2004 by Rich Harada

Those who have been reading this column for the past year or so know that digital tape provides reliable, cost-effective storage for a wide range of applications. What we haven't covered is the range of solutions offered by the tape vendor community. Given the wide array of choices available, there are two conclusions that are evident: first, innovation in the tape industry is alive and well; and second, there truly is a solution available to fit any size organization, from the home user to the smallest office to the largest enterprise data center.

Tape drive and media vendors have tailored their individual products and formats to address the very diverse needs of each type of organization. Likewise, there are automation products at the entry level, midrange and enterprise with appropriate scale and management features to meet the specific requirements of each user category and their needs.

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Customers looking for a tape solution have a great number of choices available, both in terms of drive technology and in automation (autoloaders and libraries). It should be the particular storage and data protection requirements (from the following variables) that determine the right or best choices.

Capacity: For backup applications, the capacity of a single tape cartridge, including compression, should exceed the capacity of the source disk to help manage the complexity of data recovery operations. On the other hand, the tape shouldn't be so large that most of its capacity is wasted on incremental backups. Many formats support multiple size (or length) tapes to address this issue.

Those formats with active development roadmaps will continue to see a periodic doubling of their capacity, usually every 2 years or so, to keep up with the capacity increases in hard-disk systems and the growing thirst for affordable storage options among customers.

In evaluating a drive's capacity, it is important to look at both the native and compressed specifications. All tape drives support on-board data compression--most at 2:1 and some more than that. But not all data types or applications will take advantage of this compression, so be sure to test this when evaluating your selections. For this reason, the Table and Chart show only native capacities.

Data Transfer Rate: Tape drives operate most efficiently when data is streamed to and from them at their maximum data transfer speed; the faster this rate, the shorter the backup windows will need to be, assuming the servers feeding the tape drive can supply data at that rate. Faster data transfer rates also mean faster full restore operations (less downtime when something bad happens).

Data Access Speed (Time to Data): In general, it takes longer to load a single-reel tape cartridge than one with dual reels, and then seek to a given point on the tape for data retrieval operations. On single-reel tapes, the tape leader must be engaged by the drive, fed through the drive's internal tape path, and then wound around the internal hub. This doesn't have much impact in streaming applications such as backup, but can be a big issue in random-access applications such as near-line archival and ILM. Of those listed above, DAT72, 9840C and AIT-4 have dual-reel tape cartridges and offer excellent time-to-data performance.

Library Support: In larger organizations, it will be important to find automated library products that support the chosen drive technology. There are many choices for libraries at many different capacity points, with varying support for one or more drive types, sometimes allowing combinations of different drives within a single library. Be sure to account for anticipated growth during the life cycle of the system: but given that drive and media technologies may improve through several generations during the life of the library, the potential capacity of the library should grow substantially over time.

For small office environments, a single tape drive perhaps networked through a backup or application server, might be sufficient for all data protection and archival programs. In slightly larger operations, an autoloader is often used, which typically shuffles up to 7 tape cartridges to a single drive.

The next larger range of tape automation is sometimes referred to as an entry-level or mini-library. These boxes contain between 10 and 25 tape cartridges and either one or two drives. Some vendors enable stacking of multiple mini-libraries, with a mechanism to move media between them, to create larger, scalable systems.

Next up are the mid-range libraries, holding anywhere between 30 and 1,000 tape cartridges, and from one to several dozen drives. These units are often highly configurable and field expandable, and may come with specialized management software. Some models even allow partitioning of the drives and media into logically separate devices to support diverse applications (such as backup or archive) that cannot natively share tape storage resources.

The high end of the automation market, supporting large enterprise data centers, includes a selection of devices that can scale to over 6,000 media cartridges and hundreds of drives. These units come in two forms: the "silo" and the "rail." Both units are state-of-the-art in management and virtualization software, and have high-availability capabilities to support the most demanding customer applications.