Tale of the Tape

Not long ago, tape storage technology seemed to be down for the count. The growing demands of electronic storage'for imaging, multimedia, streaming video and other data-intensive applications'led people to question whether older generations of tape drives and libraries could compete with fast-growing optical technologies.But recent developments in the technology have helped tape libraries get back on their feet in large enterprises.Enterprises need storage technology that is cost-effective, delivers media investment protection and fits with current and future needs. No technology better meets these requirements than tape, according to a research report from the Aberdeen Group, a computer and communications market research and consulting organization in Boston.Aberdeen and other analysts point to a new generation of drives that uses cartridges with much higher storage and throughput capabilities, higher quality tapes and higher data-compression ratios than ever before.These super drives let tape library manufacturers make better, more cost-effective and highly scalable libraries. By adding drives and tape cartridges to a base model, you can scale tape libraries from 100G or so of storage to terabytes of data'or even petabytes if four or five more units are added to the base library.[IMGCAP(2)]To understand tape libraries, it helps to understand how tape autoloaders work. Basically, they are small libraries that manage a few gigabytes of data. Autoloaders have one drive that typically handles fewer than 10 tape cartridges. A robotic arm is used to pick and place the cartridges in the correct slots. Autoloaders are excellent devices for small organizations requiring unattended backup for a week or less.Tape libraries can hold much more data than autoloaders and generally have more than one drive. As a rule, the enterprise libraries listed in this guide have between two and 10 drives but can be scaled to handle 20, 50 or more drives. The maximum number of cartridges ranges from several hundred to thousands in the case of Grau Data Storage AG's ITL-XL (4,032) or Sun Microsystems Inc.'s StorEdge L5500 Tape Library (5,500).Many tape libraries feature multiple built-in SCSI buses to maximize direct-attach throughput, and features such as filtered air systems, individual drive cooling fans, brushless motors, self-calibrating digital servo control systems, lockable front doors and inventory sentries.Selecting the right tape drive is a tricky business. While there are more and better formats than ever before, none are perfect for all your needs.But there is some common ground among all tape drives, including:Data compression. Compression of at least 2-to-1 is built into most drive hardware. In addition, a handful of third-party software vendors offer software compression. Look for a compression ratio of 2-to-1 or 3-to-1 from most drives, but since the compressibility of various data types can vary widely, don't expect exact ratios to prevail.Cartridge types. Two types of tape cartridges are now available: single reel and dual reel. Space doesn't permit a review of all the details; suffice it to say that single reel cartridges are better than dual reel for overall capacity, and dual reel cartridges perform better.Recording technology. Linear parallel recording writes data in parallel on multiple tracks simultaneously. Linear serpentine writes data along one channel on the tape and then reverses direction to write another channel. Helical scan recording records data in stripes at an angle across the tape.Software support. Most tape drives support popular operating systems and come with proprietary backup and recovery software. Third-party providers play an important role in developing backup and recovery software that can be ported to tape libraries.Drive size. The 5.25-inch form factor has long been a favorite among vendors, but the newer 3.5-inch format has become increasingly popular among vendors that want to increase the number of drives in a library without increasing the size of the drive bays. Many older enterprise-class drive technologies still come in formats even larger than 5.25 inches.Interconnections. Various flavors of SCSI have long been the favorites for attaching drives to host platforms or libraries, with 1G and 2G Fibre Channel interfaces becoming popular for connecting tape libraries to network-attached storage or storage area networks.Auxiliary memory. The latest generation of tape cartridges, such as Sony Electronics Inc.'s AIT-3 series and Ultrium LTO, come with nonvolatile memory chips that contain metadata about where key information on the tape itself can be found. Sony's Memory-in-Cassette, or MIC, allows the AIT cartridge to load media faster and doubles the file search performance of other tape systems.Media type. Some drive vendors have developed advanced tape media to work with their drives. A consortium formed by IBM, Hewlett-Packard and Seagate developed LTO Ultrium tape to work specifically with its LTO drives. And Sony, with its Advanced Metal Evaporated technology'which increases the active magnetic material on the tape'could have the most highly developed tape architecture yet.To look down the road, manufacturers are developing newer generations of drives that will increase capacity, performance and speed.Sony has plans for much faster drives, including its new Super-AIT (S-AIT) series, which produces 500G of capacity by using 5.25-inch drives and higher compression ratios.Meanwhile, Quantum's plans include the Super DLT 2400 drive, scheduled for release in 2006. Its native capacity will be 1.2T with a 200-Mbps transfer rate.And the LTO Ultrium migration path calls for development of a Generation 3 that will provide 400G of native capacity and 40-Mbps to 80-Mbps of throughput. Plans for Ultrium Generation 4 call for doubling those numbers.