SATA opens its doors to tape.

The SATA interface has become synonymous with hard disk drive (HDD) solutions that deliver performance and reliability at a price typically below the cost of SCSI or Fibre Channel. Popularity for the SATA interface has been growing at a break-neck pace. In fact, IDC reports that SATA is slowly overtaking both SCSI and Fibre Channel within the HDD market.

The Parallel ATA (PATA) camp is also feeling the SATA heat. This standard has served the storage industry well for years, but users are demanding faster performance, higher reliability and improved physical flexibility.

SATA proliferation is only set to expand. Tape storage drives are ripe to take advantage of the various SATA benefits, and Sony Electronics is again at the forefront of the industry. The company is currently developing SATA-based tape drives within its AIT (Advanced Intelligent Tape) family.

Understanding the SATA Specification

SATA, or Serial ATA, is a point-to-point connection using a thin cable. Unlike cumbersome PATA ribbons of the past, SATA cables use only seven wires. Four wires are dedicated to communicating between the drive and the computer. Two wires transfer data from the computer to the drive (downstream), while the other two transfer data from the drive to the computer (upstream). The remaining three are ground wires.

The small size and greater flexibility of SATA cables deliver several benefits. The primary benefit is the higher levels of physical functionality offered to storage administrators and integrators. SATA cables take up less space than PATA ribbons and can carry data a little more than three feet, much longer than PATA's limited eighteen inches. The thinner cables also eliminate the restricted airflow often caused by wide PATA ribbons.

There are three generations of SATA currently available on the market. SATA 150 is the first generation, often called SATA I. The 150 marker describes the standard's 150MB/second throughput speed. Most SATA drives currently available on the market are based on the SATA 150 specification.

The second generation is SATA 3G. The 3G is not a wireless frequency reference. The specification gets its name from an increase in speed. The 3G moniker describes a doubling of the 150MB/second transfer rate to 300MB/second--or 3 Gb/second.

The latest SATA iteration is SATA II. It isn't technically a new generation. Instead, it's more of a group of SATA features (or extensions) that can be integrated into SATA 150 and SATA 3G storage drives. The planned External SATA extension is an example. It doubles the possible SATA cable length to six feet.

Why SATA Tape Drives?

The SATA interface is a high-performance, high-quality connectivity specification. It's also extremely popular, present on almost every server motherboard shipping today. SATA-based tape drives provide a step-up for storage administrators looking to avoid slower and potentially less reliable ATAPI technology. The SATA cables have higher data integrity than the ATAPI option.

ATAPI tape drives have traditionally been five to ten percent less expensive that their SCSI counterparts, and it is expected that this cost advantage will continue with next-generation SATA tape drive offerings.

The flexibility of SATA tape drives is another benefit, ideal for non-mission critical, secondary and bulk storage applications. The interface is perfect for moving data across multiple segments, such as desktops, midrange servers, file and print servers and network storage.

SATA's flexibility and inexpensive nature has fueled the popular disk-to-disk storage architecture, especially within the small-to-midsized business market. One important element, however, has been left out of the picture. SATA tape drives are the final tier. The technology delivers a true serial disk-to-disk-to-tape (D2D2T) architecture. This option is sure to please storage admins needing to reliably back up servers and storage arrays. Tape storage offers high performance in streaming capabilities when coupled to hard disk drives in D2D2T configurations, significantly reducing network traffic loads.

The benefits of SATA tape drives go beyond a slightly lower price tag and architectural flexibility. The specification is also efficient and easier to network and troubleshoot from the IT support side of the table. The external connectivity option available with SATA II creates the possibility for a very portable and highly robust external tape drive, much like USB.

SATA tape drives also eliminate transfer rate bottlenecks experienced with ATAPI. The ATAPI specification was not designed to handle the fast transfer rates (up to 62.5MB/second) of the latest AIT generations. The drives also deliver the traditional benefits of tape, including the ability to be easily transported offsite for long-term archiving and disaster recovery.

There is, of course, a trade off. SATA is slightly slower and less extensible than SCSI, Serial-Attached SCSI (SAS) and Fibre Channel drives. The performance gap, however, is shrinking on almost a daily basis. SATA disk drives have additional trade offs surrounding disk revolution speed and reliability, but neither are an issue with tape drives.

SATA Joins the Tape Market

SATA tape drives add another specification to an already crowded set of acronyms. The market already has PATA, ATAPI, Hybrid ATA, SCSI and Fibre Channel. The SATA format, however, is a viable option that deserves a place in the tape storage mix.

The ATAPI interface is a popular option for inexpensive tape and hard disk drives. The performance and reliability issues of ATAPI have already been discussed. SATA is a more solid standard option, featuring higher reliability and performance.

Hybrid ATA is a category within the ATAPI classification. It describes ATAPI devices with a bridge mechanism, making them appear as USB or Firewire. The format still has the performance and reliability issues associated with ATAPI. What's more, SATA requires no bridge.

SATA also faces a challenger from the SCSI family. SAS promises the reduced price of a serial interface with the proven reliability and performance of SCSI. SAS doesn't compete as aggressively with SATA tape drives as the current ATAPI option. Most analysts believe SATA will ultimately replace ATAPI. SAS, on the other hand, will perform as a low-cost option for the performance niche occupied by today's SCSI and Fibre Channel drives. Most of the replacement market for SAS will come at the expense of the SCSI and Fibre Channel share.

SAS and SATA can, of course, work together to create a particularly robust storage solution. The SATA drives can plug into SAS solutions, providing additional system-level flexibility and matching cost versus performance requirements.

SATA Tape Drive Availability

SATA tape drives will soon be a reality. Sony is currently developing SATA-based AIT drives and is already in the product testing and qualification phase with a number of partners. Target availability for the drives is expected at the end of this year. The drives will be based on the SATA 150 specification with support for SATA II extensions planned for early next year. The SATA AIT drives will reach native storage capacities of up to 200 GB (520 GB compressed). This capacity, will become scalable when automated SATA tape autoloaders and libraries are developed down the line.

The SATA AIT drives are set to open a new door in the serial attached storage category. The drives will soon be on the market, completing the tiered D2D2T architecture puzzle and delivering an inexpensive and highly flexible interface option for storage administrators.

Brett Schechter is a senior manager in the Component and Business Solutions Division of Sony Electronics, San Jose, CA

www.sony.com