Tape: Alive and full of options


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Despite major advances in disk technologies, tape continues to be the mainstay of most companies' backup efforts, despite being viewed to some users as throwback technology. New capabilities such as higher tape densities, the ability to manage different tape mediums in one library and increasingly higher rates of reliability are keeping tape the most cost-effective storage medium.

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Sony introduces AIT drive for PCs
Sony Electronics recently released an external Advanced Intelligent Tape (AIT) drive for PCs and laptops with USB and i.LINK/FireWire (IEEE 1394) connectors for most PCs and Macintosh computers, as well as an internal ATAPI version for use in entry-level servers and workstations. With maximum compressed capacities from 91GB to 130GB and maximum native data transfer rates from 4MB/s to 6MB/s, Sony's new StorStation AIT drives start at $800. Sony's new external AITe90-UL drive will include a complimentary copy of IVision Software Inc's ISafe backup software for Windows.

Rick Luttrall, director of marketing for Hewlett-Packard's Nearline removable storage line of products, uses a rule of thumb to help customers determine the tape resources they need. For every 1TB of disk storage, a company should have three to five times as much tape available. While not a hard and fast rule, Luttrall finds that a 3:1 ratio gives an organization enough tape for about a month's worth of unattended backup, while the 5:1 ratio will give about a quarter's worth of unattended backup.

Assuming Luttrall's numbers hold true (see "How much tape do you need?"), these ratios should serve as a wake-up call to a silently growing cost in organizations: tape media. While an organization may upgrade their disk subsystems to take advantage of higher capacities and lower costs per megabyte, it usually fails to give the same attention to their tape technology, relying on what's worked in the past. This failure to upgrade can mean escalating costs.

For instance, older DLT 4000 tape cartridges hold 20GB of data natively and 40GB compressed, back up at a rate of about 10GB/hour natively, 20GB/hour compressed and cost $70 to $100 per cartridge. Contrast this with the more current SDLT 320 tape cartridges which hold 160GB of data natively or 320GB compressed, back up at 57.6GB native, 115GB compressed and cost about the same ($100). A move to a more current tape media can save money and shorten the backup window (see "Tape media formats").

Tape library clusters
Today's tape libraries can scale to manage terabytes of data and hundreds of tapes in one frame. In fact, an increasing number of tape library vendors are clustering their individual frames to create one large tape library unit that can scale to manage petabytes of data and thousands of tapes.

The Advanced Digital Information Corp. (ADIC) AML/2 illustrates this clustering functionality. The AML/2 comes in QuadroTower modules, nine of which may be configured as a single unit which scales to hold more than 5PB of data and 400 tape drives. It also hosts and manages multiple tape mediums simultaneously within a single frame. The 20 mediums it supports range from DLT, SDLT and LTO tape formats to 3590 and 9840 tape mediums found in high-end mainframe data processing environments.

Ever try to restore data
from 20-year-old tapes?
Tape's longevity--one of its greatest strengths--is also its greatest drawback. Managing and tracking tapes that go back decades, much less restoring the data on those tapes can become a logistical nightmare. To circumvent some of this pain, companies should follow one of two policies: First, as data is needed from older tapes, it's recalled and migrated to newer media. And secondly, even if the data is never recalled, as time passes, the data is migrated to a newer generation of tape to ensure the data remains recoverable for the foreseeable future.

StorageTek PowderHorn 9310 tape library is also a highly scalable unit. A single 9310 library may be configured to hold 1.2PB of data supporting 80 of StorageTek T9940B tape drives. While these 9310 libraries lack the wide range of multimedia support ADIC's AML/2 offers, you may configure 24 tape libraries into a single cluster that may hold over 57PB of data and 960 tape drives.

For organizations looking to consolidate their diverse tape mediums into one tape library and still use the tape medium, a product like ADIC AML/2 makes a lot of sense. In addition, most current tape drive technologies remain compatible going back a few generations. For example, the most current SDLT tape drive in the AML/2 reads information from DLT tape cartridges that go back two or three tape generations. StorageTek's tape drives support any combination of their past five generations of tape media technologies down to the individual slot all in the same library.

While these two models have some impressive features and scale to support the highest data processing environments, many other models exist that fit into enterprises of various sizes such as the IBM 3584 LTO UltraScalable Tape Library. It scales to over 2,400 tape cartridges, allowing for up to 72 tape drives in a single unit. Each of its tape drives--using the latest IBM LTO Ultrium 2 technology--support native streaming data rates of 35MB/s. The unit itself can scale up to nearly 1PB of data in a single frame assuming the use of 2:1 compression.

This was first published in April 2003

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