SDLT CTR Looks Under The Hood.

The waiting, of course, is over. Both LTO and Super DLTtape have been introduced into the marketplace. Now, time and the marketplace will decide how midrange tape integrators and users will respond to both of these late-to-market technologies. The applications that demand high-availability storage solutions are numerous, and range all over the performance/availability spectrum (See Fig).

Like LTO, Super DLT is intended to offer the superior capacity and transfer speeds needed to manage voluminous data created by current applications such as business intelligence systems.

An extension of the: Digital Linear Tape (DLT) standard, Super DLT promises capacities of up to 110GB and transfer rates of over 16MB/sec in uncompressed mode.

The obvious question is why bother with new tape formats? The answer is the explosion of data across the enterprise landscape. The Web, and its own related content explosion, is the most obvious example of why we need more storage. Tape has been lagging compared with other technologies and that is why LTO and Super DLT are important.

It is a difficult proposition to assess which technology path, LTO or Super DLT, had the roughest time coming to market from a technological point of view. LTO is a first generation technology, with the obvious challenges involving the developing of a technology from the first designs to a deliverable product. SDLT makes use of new technologies as well, and has the added requirement that SDLT, for market reasons, must necessarily be backward-compatible with earlier generations of DLT media. IBM, Hewlett-Packard, and Seagate promote LTO as an open standard, while Quantum focuses on compatibility with the installed base of DLT cartridges already in use in enterprises. Quantum said Super DLT will read well over 80 percent of the installed base of its DLT media. Quantum also asserts that Benchmark Super DLT drives will read media written by Benchmark Tape Systems' DLT1 tape drive. Tandberg Data continues as a second source for both DLT and Super DLT products.

Under Super DLT's Hood

A key efficiency for increasing capacity and transfer rate involves offering more tape area for recording, and the creation of additional tracks for recording and increased recording densities. While recording density per track is vitally important, even more important is the ability to use more of the recording surface for data.

Quantum's Super DLTtape technology addresses this efficiency. The technology behind SDLT is based on Laser Guided Magnetic Recording (LGMR) technology, which blends optical and magnetic technologies to increase the number of recording tracks on the databearing surface of the media.

Five advanced technology modules enable LGMR to increase density and make maximum use of available tape on a cartridge. These include Pivoting Optical Servo (POS) that eliminates the need for pre-formatted tape; Magneto-Resistive Cluster heads (MRC) and new high-efficiency Partial Response Maximum Likelihood (PRML) channel that deliver higher data-transfer rates and capacity; Advanced Metal Powder (AMP) media for extremely high data densities; and Positive Engagement, a robust tape-leader-buckling mechanism for high-duty-cycle automated environments.

Enabling Technology

MRC head technology is an enabling technology for LGMR. The heads are small MR heads, densely packed together to form a cluster. Clustered heads are joined together using thin film process technology. These heads provide higher transfer rates and capacity than traditional MR heads of equal size. MRC heads also provide high wafer usage efficiency for low head costs. They offer higher track density and capacity through greater resistance to environmental considerations, like temperature and humidity and they increase transfer rates and performance with multiple heads. MRC is integrated into the POS as a LGMR enabler.

The POS is likewise a core enabler of LGMR technology. It offers a combination of optical and magnetic technologies. POS is an optically assisted servo system, which combines high-density magnetic read/write data recording with laser servo guiding. Designed for high duty cycle applications, the POS has a much lower sensitivity to outside influences, which allows the Super DLTtape system to achieve a track count with an order of magnitude increase over current DLTtape products.

The POS system decreases manufacturing costs and increases user convenience by eliminating the need for pre-formatting the tape. Additionally, customers gain 10 to 20 percent more capacity that is lost due to traditional magnetic servo approaches. Super DLTtape uses a full 100 percent of the recording surface for actual data recording by using the optical servo on the unused backside of the media. This is an exception to conventional magnetic tape use in the enterprise, where a portion of the front side of the media must be reserved for servo activities.

As the media moves through the POS, the optical tracking laser follows along on the backside of the media, tracking the embedded optical targets. The POS assembly pivots around a single mounting point to keep the magnetic read/write heads aligned with the optical tracks and reading data from, or writing data to, the tape.

New PRML Channel

Originally, PRML encoding was instituted into disk drive technology to control error correction. More recently, it is being included in tape technologies for the same purpose. SDLT technology offers what the developers claim is a newer PRML channel that improves on traditional PRML disk drive technology by bringing increased performance and capacity to LGMR technology and high-performance tape drives.

The advanced, high-efficiency PRML channel used in LGMR was developed as a collaborative effort by Quantum and Lucent Technologies. It provides high encoding efficiency recording densities (97 percent efficient) for greater capacity and performance which enables Super DLTtape to substantially increase its transfer rates and capacities over current DLT iterations. Super DLT tape drives based on LGMR will use PRML from its first generation through an entire roadmap of compatible products.

Reliability

Now that both LTO and Super DLT products are available, integrators, OEMs, and users will look for proof that the technologies are dependable. One of the most important factors when selecting a tape solution is reliability. There were problems with bugs in the DLT8000. On the other hand, DLT has a large installed base as the midrange market leader. The backward-compatibility feature of Super DLT may well be the deal-maker for many remarketers.

Dependability is a greater issue than ever. Costs of downtime--that must be countered by effective use of tape technology--are growing at a breakneck pace. Popular Web service provider America Online must shoulder $3 million in rebates for a 24 hour outage. eBay suffered a 22-hour outage in 1998 that surrendered revenue of $3-5 million. While advanced technology never provides a complete answer to problems of downtime, high availability tape technology such as SDLT could represent both foundation and capstone to the battle against downtime.

Editor's Note: A complete listing of Super DLT vendors can be found on our web site: www.wwpi.com