Reliability with a roadmap: choosing a tape technology to replace DDS. (DDS Replacement).

When DDS (DAT) technology manufacturers Hewlett-Packard, Sony, and Seagate announced they would not develop the next-generation DDS product, the DDS-5, millions of cost-conscious DDS users found themselves in need of a new tape storage product alternative. Gartner/Dataquest pinned the installed base of DDS tape drives at 6.2 million by the end of 2000 with more than 1.5 million of those units shipped that same year. (Gartner/Dataquest "2001 Industry Storage Report," Fara Yale.) The DDS replacement market was born.

Addressing the Market, Filling the Need

The DDS replacement market requires a tape technology that offers high reliability at similar or greater DDS capacities and at affordable DDS pricing levels. The replacement technology must offer a multi-generation product roadmap that meets storage growth needs while maintaining DDS price points. Those burnt by the demise of DDS do not want to relive the experience.

Will This Technology Be Around in the Future?

Before selecting a tape drive, IT managers should carefully evaluate not just individual product features and capacities, but the core technology each product is based upon. The choice will impact the organization for years to come. What is this technology's product roadmap? Is it extendible in both capacity and transfer speeds? What are the barriers to the technology reaching its full potential in future iterations? Is the company behind the technology aggressively working towards next-generation products ahead of competitive technologies?

Many IT managers chose to employ legacy tape technologies like DAT and Travan based solely on their long histories and affordable prices. The result is a frightening scenario of incompatibility between tomorrow's drives and the past decade of data, as these technologies are reaching the end of their lifecycles.

How Much Faster?

How Much Capacity?

How Much?!

Developers of new tape technologies always charge out of the gates exclaiming how much faster and higher in capacity their drives are than the competition. In doing so, a major problem is being overlooked--the price for these new tape devices can be several times the price of the servers they are backing up. Choosing a $5,000 DLT drive to back up a $1,000 entry-level server just doesn't make sense.

Finding Reliability and Capacity at an Affordable Price

In the wake of DDS, users looking to migrate from the dying technology to one of many on the market seek three core characteristics. Reliability is crucial and central to the mission of backup. Corrupt or inaccessible data negates the purpose.

As hard drive capacities steadily increase, more and more data is being stored to disk. Therefore, more and more data must be backed up. ADR2 technology brings entry- to mid-range-level server-to-backup price ratios back in line, by offering the reliability and capacity of a new tape technology at a sub-thousand dollar price point.

OnStream's ADR2 is the second generation of the company' s award winning Advanced Digital Recording technology. Achieved by coupling proven technologies with the company's continued development in advanced recording heads and tape density, ADR holds promise for several generations to come. Based on an eight-channel array head technology, ADR2 provides the ability to read or write eight tracks of data simultaneously. The data reliability is one error in 1019 bits, which is 10,000 times better than the common tape standard of one error in [10.sup.15] bits.

The exceptional reliability, capacity and performance of ADR2 technology is possible at a low cost due to four separate tape storage innovations: buried servo signaling, multi-channel recording, true variable transfer rates and enhanced data integrity.

Buried Servo Signaling Gives Precise Tape Position Information

ADR2 technology's biggest innovation is an advanced, buried servo system in the media that contributes to the highest data reliability levels of any entry- to mid-range server-backup tape device.

The buried servo system ensures data integrity by guaranteeing accurate tape tracking. During the manufacturing process, the low-frequency proprietary servo signal is written deep within the media layer. During customer use, high-frequency user data is written on top of this servo signal. The servo signal is a series of sine waves that provide precise feedback to control the position of the read/write head on each of the 384 data tracks across the width of the tape. During the read or write process, the head detects the sine waves' amplitude and phase to determine the head's lateral location on the tape and makes corrections to keep it on track.

While the head is writing, the embedded servo signal is also used to ensure data integrity. If the head detects a perturbation on the servo signal due to an off-track condition, or degradation of the signal due to loss of head to tape contact or damage to the media surface, the drive will immediately stop writing to ensure that data on adjacent tracks is not overwritten. The drive then initiates a re-write operation to ensure that the data is written correctly.

Multi-Channel Recording Increases Media Life

ADR2 technology allows the drive to reduce the speed of the tape under the head by a factor of eight when compared to single track drives. The lower tape speed results in gentle tape handling that improves the life and reliability of the drive and media. At slower speeds, less power is required from the host and less friction is generated from media to head contact, resulting in a lower overall temperature and less media wear. Lower speeds also allow ADR2 drives to run at the mid-40 decibel sound range--barely detectable in an office environment.

By reading eight tracks simultaneously, all 384 tracks of an ADR cartridge can be read in 48 end-to-end passes. A typical single-track drive requires 106 end-to-end passes to read all 106 tracks on its media. This gives ADR media a significantly longer life expectancy since tape life is generally expressed in terms of total end-to-end passes.

True Variable Transfer Rates Optimize Throughout

A traditional issue with tape technology has been that systems supply data at variable rates while tape drives write at a fixed rate. To compensate, a tape drive does one of two things when data is not reaching the drive fast enough: 1) In a process commonly known as back hitching, the drive will stop, back up, reposition itself and continue writing when more data arrives. This continuous start-stop cycle can cause unnecessary drive and media wear, and the degradation of tape tension can cause catastrophic data loss. 2) Other tape drives reduce their transfer rate when the data transfer rate slows. This causes degradation of performance because typically the drives cannot increase speed again until they reach the end of the tape and reverse.

ADR2 technology, however, allows infinitely variable tape speeds that can support data transfer rates anywhere between 0.5MB/sec to 4MB/sec.

Improved Error Correction Enhances Data Integrity

Older tape technologies have to run a separate verification pass after the data is encoded--effectively knocking transfer speeds down to half the nominal speed and cutting the tape lifespan in half-to ensure data reliability. Many of the current high-performance tape drives use a ReadWhile-Write feature that enables them to read, to verify data integrity, while writing. This requires the incorporation of dual gap heads with extra read verify circuitry resulting in increased product costs of approximately 25% and, of course, extra complexity.

The OnStream ADR2 uses the servo signal innovatively to give the same level of reliability as Read-While-Write without the traditional hardware complexity. With OnStream's ADR media, the servo signals lie underneath the data and are used as an indicator for media integrity. As the head writes data, it also is detecting the servo signals. If the servo signals are absent, the system maps the region as defective and re-writes the data. This approach allows ADR2 technology to achieve data reliability without sacrificing speed, tape life or price.

Tape devices improve data integrity by scattering ECC (error correction code) bits across the data track. Mathematical algorithms can then use the ECC to reconstruct missing data bits. ADR2 technology's superior error rates are a result of its ability to read and write all eight tracks at once, which makes it possible to distribute error correction code spatially, that is, both horizontally and vertically across eight tracks. This allows data to be recovered from a tape with wide scratches across its width or even with a single track wiped off the entire length of the tape.

www.onstream.com

Bill Gerstner is VP and GM of US. sales and operations at OnStream Data (Austin, Texas)