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ATA and SATA drive usage goes beyond expectations.

ATA and SATA technologies are experiencing increased application usage with the newer generation of drive products. Previously relegated to use in desktop workstations. ATA and SATA drives are now being deployed for more challenging applications due to the many benefits of today's ATA products. ATA drives are proving their worth in many server environments, where high-capacity storage and rapid data retrieval are required. As these markets grow, one might ask if there is the end to the infiltration into the SCSI and FCAL drive markets. As technology continues to become more powerful, one might further ask if there is a reason why ATA drives can't be configured to address even the most demanding reliability and performance disk storage requirements.

Pricing: The Initial Motivator

Why is there such a movement towards the use of ATA drives use in an increasing array of applications? Without a doubt, the prime motivator is price. Many RAID system developers have tracked ATA (previously called IDE) drive pricing for years.

In 1998, an analysis conducted by Medea Corporation showed that state of the art IDE drives were 28 Gbyte, whereas the SCSI drive technology was at 36 Gbytes. Unit pricing at that time was $250 (USD) for the IDE and $1200 for SCSI, or $9/Gbyte for IDE and $33/Gbyte for SCSI. SCSI was 3.6 times the cost-per-Gbyte.

Today, the pricing delta has widened significantly. ATA drives are now available for a mere $.60 per Gbyte while SCSI drives cost $4.20 per Gbyte. SCSI drives are now 7 times more expensive than ATA drives. How could any company that is focused on the bottom line ignore the prospect of saving up to 86% on the next 1-terabyte of disk storage? The answer lies in the trade-offs associated with changing drive technologies and the often arduous task of altering previously held notions--even if those beliefs are no longer correct. Reliability and performance standards must also be met for the ATA application to be addressed comprehensively.

The Stigma of ATA Drives

Okay, let's get this out in the open first. For a long time, ATA drives were thought of as inferior products with lower performance and inferior reliability. These "cheap" drives were perfect for the single user workstations where data loss was not critical, performance was low and up-time could be compromised. No doubt, this has been the prevailing opinion of ATA drives in the past, but is this an accurate assessment of the technology today? The answers, which will follow, will say, "No."

ATA Drive Attributes

Whereas pricing advantages initially started the movement towards the application of ATA drives in widening market arenas, there are several other attributes that each provides ATA technology with additional compelling advantages, depending on the application.

Capacity

ATA drives, once thought the smaller capacity product when compared to SCSI drives, have made substantial strides in storage capacity, overtaking other drive types. Today, 250-, 300- and 400-Gbyte ATA drives are prevalent, and a 500-Gbyte product is on the immediate horizon. SCSI and Fibre Channel drives are only now introducing 300-Gbyte options. For high-capacity applications, this means less spindles may be required.

Power Consumption

ATA drives consume as much as 40% less power than SCSI equivalents. Less power consumption equates to less heat generation from power supplies and drive arrays. This is an important advantage because it allows for a denser population of drive arrays and coupled with higher spindle capacity, the result is significantly reduced rack space over other drive types.

Shock and Vibration

Shock handling characteristics of ATA drives are also superior. When comparing 3.5-inch media, the operating range is typically 29% better than SCSI drives, and the non-operating modes over 50% better at 350 Gs, compared to 225 G's of SCSI drives. Two-inch ATA drives have even an even higher advantage at 800 Gs.

Addressing The Negatives Quality

Let's get back to the "cheap drive" stigma of the ATA product. Indeed, they are much less expensive--nearly 1/7 the cost in some cases. However, cheap carries with it the connotation of low quality and low performance. Drive reliability is usually measured using two specification points: MTBF (Mean Time Between Failures) and Bit Error rate, (the rate at which a drive will make an error). The higher the MTBF and the lower the Bit Error rate, the higher the overall quality of the drive. Approximately 10 years ago, disk drive engineering gurus established an MTBF rating for SCSI drives which drove the MTBF calculations over the 1 million/hour mark. ATA drive products lagged for several years since such calculations were not necessary designed for the desktop market. But with improved product construction and increased engineering fervor on the part of manufacturers, today's specifications now rival those of SCSI and Fibre Channel drives at 1 million hours. Bit Error rates of ATA drives now also compare favorably with the SCSI products at 1 in [10.sup.15].

Performance

Performance remains an area where SCSI drives have an advantage over ATA drives. SCSI drives possess spindle rotational rates of 10-15K RPM and outperform ATA drives, which operate at 7200 RPM. Transfer rates, although better in SCSI drives, are in fact only 20-25% faster than ATA drives. These performance characteristics are notable because they help dictate some of the areas in which SCSI drives are still favored over ATA counterparts. Heavy random reads and writes of short records remains the domain of SCSI technology. But as record sizes increase, and the degree of randomness of data lessens, ATA technology performs very well and is becoming an alternative worthy of consideration for many users.

Applications for ATA Storage Products

Obvious applications for ATA drive use are disk-to-disk back-up and near-line storage systems. Several leading storage providers have exploited low cost-per-Gbyte and dense packaging advantages in reference material storage systems and quick disk back-up solutions. These applications are well suited for ATA. Both applications require very large storage capacities and limit the degree of random data transfers or I/Os per second. But what about deploying ATA products for more challenging, mission critical applications? Companies are finally realizing the impressive capabilities of today's ATA and SATA drives and are incorporating them into increasingly challenging applications such as image and data acquisition systems, medical imaging, and 24X7 broadcast severs.

Medea Corporation and Storage Concepts, Inc. were two pioneers in moving ATA drives off the desktop and into more demanding storage applications. Medea created ATA-based RAID 0 products for the video market in 1997. Storage Concepts introduced RAID 3 and 4 protected-storage ATA-based products for high-end video, geo-spatial, aerospace and medical applications in 2000. These companies tolerated the lowly impressions and misconceptions of ATA drive technology, and demonstrated early on that ATA drives could be used effectively and profitably in an expanding number of market segments. The challenge became to make these products reliable and explain the benefits of this reliability to different markets.

Medea's expertise is focused primarily on the use of ATA drives in real-time performance applications, such as the growing field of High Definition (HD) uncompressed video and critical image capture for medical modalities such as X-RAY and CT scanning. Using ATA drives in these markets requires extensive drive certifications and controller technology to increase data rate handling, such as Medea's MST Multi-Stream Caching algorithms. Medea's arrays operate in real-time to protect the speed of the write and read in the even of a drive loss in a large array. The controller itself is a completely redesigned architecture, which addresses the ATA drives specifically, exploiting their advantages and accommodating the performance differences.

Medea has also employed ATA drives in rugged and extreme environments, taking advantage of the impressive shock ratings of these drives. The Medea RAID Shuttle is an array of five drives, configured with RAID protection, and will support continuous data transfers up to 200 MB/sec. This ATA-based solution employs four 2 Gbit Fibre Channel host ports for easy connection to performance environments. Since the RAID Shuttle is often deployed in severe and mobile applications, the low power consumption feature of ATA also proves valuable and allows for tight packaging for tight spaces where the product will be used.

Likewise, Ampex Corporation has found the ATA drive to be effective in rugged environments for the Military/Aerospace market. Ampex utilizes the 2.5-inch form factor ATA products. These drives, designed for mobile applications, have shock ratings as high as twice that of SCSI drives. Paralleling these drives allows Ampex to address applications that previously used very costly semiconductor memory. Ampex's DSRs 440 is designed for airborne applications requiring high data rate and high capacity in a small, lightweight package.

In a different arena, an excellent example of ATA technology for 24X7 server applications is the Pinnacle MediaStream video server. Pinnacle, a recognized leader in developing broadcast TV servers, utilizes ATA drives in a sophisticated RAID array for on-air broadcast applications. The Pinnacle MediaStream server incorporates all of the features required for fault tolerant operation, including all redundant replaceable components and real-time guaranteed operation in the event of drive failures. Since broadcast video servers require exceedingly large storage capacities, Pinnacle's customers benefit from the drastically lower price point offered by ATA drive technology.

The future for ATA drives looks bright and the use of this technology will likely continue to proliferate as long as the staggering difference in cost is realizable. One of the key reasons for the price delta is the volume at which ATA drives are produced. Over 10 times the amount of ATA drives are built when compared to SCSI and FC drives. With more and more applications taking advantage of the new generation of ATA and SATA drives, the delta is likely to increase.

Martin Bock is president of Medea Corporation (Woodland Hills, CA)

www.medea.com
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Article Details
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Title Annotation:Storage Networking; Serial Advanced Technology Attachment
Author:Bock, Martin
Publication:Computer Technology Review
Geographic Code:1USA
Date:Mar 1, 2005
Words:1631
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