The technology of tape automation - Tape/Disk/Optical Storage

Computer Technology Review, Feb, 2002 by Kevin C. Daly

This year, 2002, is the 40th anniversary of the automated tape library (ATL). IBM delivered the Tractor system to the National Security Agency early in 1962. This massive system which contained six tape drives and 360 15-pound tape cartridges was used continuously for 14 years. It is a measure of the vitality of this technology that the capacity of the Tractor system (43GB), which was unheard of at the time, is a fraction of the capacity of a single cartridge in a state-of-the-art automated tape library today.

Automated tape libraries have played an increasingly important role in data protection solutions over the intervening four decades. While there were a number of special-purpose systems introduced in the early years, it was a series of key developments beginning in the mid-1980s that have led to today's ATL market which IDC estimates will reach 100,000 ATL shipments per year by 2003. IDC forecasts an additional shipment of more than 160,000 single-drive "autoloaders" per year by 2003.

The first critical technology was digital cartridge tape, introduced by IBM as the 3480 tape system, in 1984. Automation systems to support the 3480 tape system became available very shortly later. The 3480 provided, for the first time, a standard tape system that was amenable to automation; a system that has survived in a highly-evolved form to the present day.

Several years after the 3480, Exabyte introduced a very high-density tape system based upon the commercial 8mm tape cassette. This system adapted helical recording techniques that had been developed for video recording to provide digital recording at very high densities when contrasted with the linear recording techniques that had traditionally been used for digital recording. Once again, the cartridge tape format permitted the introduction of automation systems to support the 8mm cassette format soon after the initial introduction of the format itself. Once again, this format has proven durable. Both the Exabyte system and the AIT 8mm system from Sony have technical roadmaps that suggest they can meet a range of needs for a considerable time to come.

One of the most significant developments in this area was the introduction of a high-density digital linear cartridge tape format, called DLT, by Digital Equipment Corporation in 1992. This format drew from the low-density DECtape technology, but provided density and cost advantages that rivaled helical tape systems while retaining the linear tape technology that was extensively used in the computer industry. DLT tape was sold to Quantum Corporation in 1994 and rapidly became the defacto standard tape system for the rapidly-growing network computing market. Automated tape libraries for DLT were introduced in 1994 by ATL Products, Inc.--now a part of Quantum Corp. At present, DLT-based systems represent more than one-half of the installed base of automated tape libraries and an even larger percentage of the growth of the installed base.

The most recent development has been the introduction in 2001 of two very similar high-performance tape systems: a new generation of DLT (called Super DLTtape--or SDLT) and a rival high-density linear cartridge tape system (called Linear Tape Open--or LTO) introduced by a consortium of industry partners including HP, IBM, and Seagate). SDLT and LTO tape cartridges are very similar and both have been supported by automation from their introductions.

While all ATLs share common technological challenges, the dominant issues for ATL design and implementation have evolved significantly over time. We will briefly discuss below some of the dominant issues over the past 15 years.

ATLs represented highly complex electro-mechanical systems in an industry that, on the whole, was moving rapidly to purely electronic systems. The function of transporting, importing, and exporting data cartridges was one of the last physical activities left in the data center.

Since a key element in the economic justification for tape automation was the elimination of expensive manual intervention, reliable autonomous operation of ATLs has been a critical requirement from the very beginning. At the same time, the complex kinematics required by the ATL function made it prohibitively expensive to use the traditional redundancy techniques that had been applied successfully to many other technologies. As a result, all components of ATLs had to be designed and tested for very high reliability. While the design techniques to achieve the required reliability were well-established, the testing required to gain an appropriate level of confidence in ATL reliability has remained a major challenge for ATL manufacturers since the electromechanical nature of these systems precludes many of the accelerated testing techniques that are available for electronic systems. At the present time, the large ATL installed base has provided a very high level of confidence that these systems have achieved a level of reliability that represents an effective economic balance for their applications.