Tape Feasts On All-You-Can-Eat Data Banquet. And Enjoys - magnetic tape industry - Technology Information

Computer Technology Review,  June, 2001  by Fred Moore

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The magnetic tape industry is building the foundation for the third era in its near 50-year history. The first era began in 1952 when IBM delivered the computer industry's first tape drive and lasted for 35 years. This phase was defined as the era of manual tape handling (mounts & dismounts) and the primary application for tape throughout this period was data backup.

The second era began in 1987 and was re-defined with the successful arrival of robotic libraries providing automated tape services for what had been a very labor-intensive industry. This era was referred to as the Nearline era and was successfully pioneered by StorageTek. Nearline soon became the defacto standard name for the layer of storage between online and offline storage. The resulting benefits from these automated storage services eliminated many of the troublesome growing operational aspects that manual tape faced since its inception.

The third era of intelligent tape storage is beginning. With the world producing between one and two exabytes (lx[10.sup.18]) of digital data every year, the need for mass storage capacity is obvious. Disk and tape are the two most widespread storage devices in use today. It is estimated that nearly 90% of the world's digital data presently resides on removable storage devices, primarily tape, with magnetic disks containing the remainder. Where does tape optimally fit and what architectural enhancements should the tape industry make in order to remain the primary mass storage technology? The price per megabyte purchased for automated tape storage today ranges around 1/25th the price per megabyte purchased of disk storage. In contrast however, tape storage has some limitations compared to disk. Tape access takes seconds versus milliseconds on disk to access the first byte of data and tape can only store and retrieve data sequentially. Since the majority of digital data is accessed relatively infrequently, the need for an improved mass storage system that meets the growing needs of the future has arrived.

Several data storage technologies are positioning to capture significant share of the exploding mass storage and data archive market. Today, tape is the primary choice. To respond to the challenge, the tape industry is looking at several new features and capabilities that improve its value proposition.

1. Price per megabyte. Current recording improvement rates for tape now shows a path to get to 6 gigabits per square inch. Areal densities may ultimately approach 20,000 TPI (tracks per inch) with prices less than $.0005 (five one-hundredths of a cent) per megabyte purchased by the year 2007, staying well below the price per megabyte purchased curves of disk drives. Media prices for new high-capacity tape range from $75 to over $150 per cartridge or about 1/15th of a cent per megabyte for a 100-gigabyte cartridge. Reliability estimates for emerging high capacity tape drives typically range from 200,000 to 300,000 hours between failure.

2. Tape arrays. Technologies borrowed from disk products are increasingly finding their way into tape products such as tape arrays, which can boost performance and capacity while improving data integrity through fault tolerance. Tape arrays are just beginning to arrive and borrow the basic concept from RAID disk arrays. Early tape arrays have been implemented in software but advanced, larger scale implementations may be built in the tape control unit. Tape arrays offer a "multiplying" capability for data rate and capacity while offering striping, mirroring, or striping with parity across tape drives.

An emerging architecture for tape subsystems and certain data transfer-intensive applications, tape arrays allow enhanced data reconstruction and enhanced integrity. Tape arrays may consist of data records or blocks that are striped across (N) cartridges on (N) drives providing data transfer concurrently streaming across multiple tape drives. Data is striped across cartridges and drives in different libraries to provide parallel mounting to occur though mount time is not a major issue in data transfer-intensive applications. Though desirable, an automated tape library is not required for tape array implementation. Mirroring allows two identical tapes to be created in parallel at geographically different locations. As was the case for disk arrays, tape array levels are now being defined and include levels 0, 1, 1/0, 3, and 5. The terms RAIL (redundant arrays of independent libraries) and RAIT (redundant arrays of independent tapes) now commonly describe this concept. Tape arrays address certain throughput int ensive applications and are now appearing for large files and should play an increasing role with streaming video.

3. Capacity/performance. Increasing tape capacity without providing corresponding improvements in tape data rate pushes magnetic tape into more of an archival technology niche. This limits tape's role as a technology that can provide timely access to enormous volumes of data. Therefore, tape data rates and overall throughput capability must keep up with the growth of tape capacity. Further advances in thin media and recording heads are appearing in vendor roadmaps that lead to native (non-compressed) tape cartridge capacities reaching 800GB and data rates up to 100MB/sec over the next five years for both linear and helical scan formats. The ability to store data on tape is important; the ability to retrieve it in a meaningful timeframe has become business critical. "Business resumption is now the killer app for tape".