SAS/SATA Compatibility Hits its Stride

Author: Daniel D. Reno, Senior Strategist, Marketing and Strategy, Enterprise HDDs
Hitachi Global Storage Technologies

As noted by Gartner Group in the recent SCSI Trade Association (STA) press release, Serial Attached SCSI (SAS) adoption rates experienced a significant increase in 2006, and SAS is expected to overtake Ultra320 SCSI, or Parallel SCSI, as the interface of choice for a variety of enterprise storage applications this year. Key drivers of SAS adoption have been reduced backplane complexity and improved signal integrity leading to greater reliability. In addition, the interface enables higher data transfer rates and improved scalability over Ultra320 SCSI.

SAS interface compatibility with Serial ATA (SATA) hard drives has been an added benefit, driving overall adoption rates, particularly with the explosion (since 2005) of SATA hard drive use for secondary storage. This ramp is expected to continue given that highest-capacity (one-terabyte) enterprise SATA hard drives recently began shipping in volume.

The combination of high-performance SAS hard drives and ultra high-capacity SATA drives gives builders of these mixed-interface systems and their customers the best of both worlds: tiered storage that is optimized for both performance and reliability, and cost and capacity.

Facilitating SAS/SATA Compatibility
The road to effectively building SAS/SATA systems has not been without difficulty.
A significant impact on the success of SAS/SATA systems has been the use of desktop SATA hard drives not suitable for the more rigorous enterprise environment. Performance degradation can result when users attempt to integrate desktop SATA hard drives, which are intended for single-user applications, into SAS/SATA systems. The high rotational vibration environment of multi-HDD systems, in general, has a negative impact on SATA drive performance.

True enterprise-class SATA hard drives, which first began shipping in 2004, are specifically designed to tolerate this high rotational vibration environment and carry higher reliability expectations more closely associated with traditional enterprise-class hard drives. As an example, enterprise SATA hard drives are built with technology to minimize the effects of rotational vibration, as well as other capabilities that are specifically designed to maintain high levels of performance and reliability in enterprise environments.

Another key factor in facilitating SAS/SATA compatibility, as noted in the case study with Germane Systems below, is the development of a supplier ecosystem to support SAS/SATA systems. The number and breadth of suppliers for cables, expanders and controllers has taken some time to grow, as has the general industry knowledge-base, and this has impacted the speed of SAS/SATA system adoption. Over the last year, SAS development has matured significantly, with a large supplier base, from hard drive companies that supply 2.5-inch and 3.5-inch SAS and enterprise SATA drives for these mixed enterprise environments, to vendors who supply controllers that enable the mixing and matching of SAS and SATA drives in a single storage environment. If the recent rate of new product announcements is any indication, this ecosystem has reached critical mass.

Case Study: Germane Systems Makes SAS/SATA Compatibility Work
Germane Systems is a Virginia-based company that designs and manufactures computing systems for rugged military applications. The company’s servers and storage systems are used primarily onboard Navy ships for a number of different systems like sonar and radar installations, managing both mission-critical and non-critical data. Germane deploys SAS and SATA hard drives across its product line and uses both 3.5-inch SAS and SATA hard drives in its storage arrays.

Germane has been incorporating SAS and SATA drives in its storage systems for about a year. Early on, the company faced several hurdles as it began to design and manufacture these systems. The infancy of SAS, at the time, was an issue. The company found a lot of complexity with respect to cables, expanders and other elements and very few suppliers had yet to enter the market.

“When we first began building these systems, it was very difficult to find anyone who was knowledgeable—as we started to build SAS arrays, there were no vendors supplying commercial expander cards,” said Robert Nase, director of integration at Germane Systems. “We had to quickly learn about all of the options for SAS environments. Now, there are a greater number of vendors who have more knowledge about how to build SAS systems.”

Today, Germane Systems’ customers have realized many benefits through the ability to deploy SAS/SATA storage arrays. Its customers are using these mixed-interface systems for archival and mission-critical storage. As an example, they may have a database application that has a portion of the associated data rotated to secondary storage.

“Prior to the proliferation of SAS systems, our customers had to go exclusively with SCSI-based systems and this impacted flexibility in cost and application. With our SAS/SATA-compatible systems, we have many more options to offer our customers. We can change the proportion of SAS and SATA drives depending on how their needs change and evolve. This gives our customers many choices with respect to cost per gigabyte and storage density,” Nase concluded.

As the SAS market continues to mature and further penetration occurs, these systems will continue to displace Ultra320 SCSI as a primary option for tiered storage environments. The opportunity to deploy flexible and cost-optimized SAS/SATA storage arrays means IT departments can more effectively manage budgets and extract the best return on investment in storage resources.

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