The interface used to connect a system´s CPU to a storage device is critical to a user´s overall system performance. For success, the I/O interface’s cost, data throughput performance, reliability, flexibility, robustness, and ease of integration and migration must be balanced with the needs of the user.
Since the early 1990s, Parallel ATA´s key advantages of low cost and appropriate performance have made it the predominant standard for desktop PCs and workstations. However, today´s growing use of data-intensive applications has put pressure on Parallel ATA technology to keep up. New, more powerful applications coupled with faster and cheaper CPUs have created a demand for a more capable and scalable storage I/O standard.
Traditionally, a key differentiator between I/O standards has been the cost/benefit trade offs between performance, reliability, and data protection (RAID capabilities). In general, higher-performance I/O standards with RAID have been used in enterprise environments, while lower-cost I/O standards without full RAID are used in more price-sensitive markets. In the sub-entry server, desktop PC, and workstation markets, high-performance I/O and RAID interfaces have not been used – until now.
The emergence of Serial ATA as a new I/O standard for direct attached storage changes the traditional cost/benefit equation, and the addition of powerful, yet cost-effective RAID capabilities alters the landscape for low-cost server storage.
The Emergence of Serial ATA for Low-Cost Servers
Serial ATA has been designed as the next-generation storage I/O standard for budget-constrained users, with a roadmap of accelerating performance and new capabilities to make RAID even more cost-effective. Serial ATA incorporates a number of important enhancements that deliver new benefits for users, including:
• High-performance roadmap. The first generation of Serial ATA offers 1.5 Gigabits/sec data throughput speed – faster than the most advanced Parallel ATA speed – eventually rising to 6.0 Gigabits/sec.
• Low cost. Serial ATA is designed to be cost-competitive with equivalent Parallel ATA solutions, which brings the attractive cost scaling of a desktop standard to the low-cost server market. Serial ATA hard disk drives (HDDs) are expected to maintain their cost advantage over SCSI drives (though SCSI drives will continue to be more reliable and higher-performing for high-transaction volume, mission-critical environments), making the benefits of Serial ATA RAID arrays more attractive for small business.
• Simplified connections. With Serial ATA, storage is directly connected to the backplane, making adding and removing devices safe, easy, and reliable for users.
• Better cabling. Thin flexible cables eliminate Parallel ATA cable clutter, enabling space-saving, smaller footprint Serial ATA servers.
• Point-to-point connection. Serial ATA provides a separate connection path between the host and each device so that devices can transmit data in parallel, without jumper settings or external termination, again, making RAID configuration easier.
• Command optimisation. Commands to a device are queued-up for immediate execution, without having to wait for responses and increasing performance.
• Backward compatibility. Complete software and driver transparency with Parallel ATA, makes for faster migration from the old standard to the new, and without additional migration costs.
In the past, features of this calibre have not been available to low-cost user environments because of the limitations of the Parallel ATA standard. Because Serial ATA cost-effectively eliminates these technology restrictions, the adoption of Serial ATA by desktop PC, workstation, and sub-entry server users is expected to grow.
Added Value of Serial ATA RAID
RAID is an industry standard, flexible method for maximising the protection and availability of stored data. RAID requires multiple independent HDDs managed as an array in order to write data so that it is striped across the different drives for better performance, fault tolerance, and redundancy. When RAID functionality is added to the higher throughput speed and lower cost of Serial ATA, it becomes a very cost-effective way to boost the quality of data protection, availability, and reliability for small business users.
While Parallel ATA RAID implementations certainly remain viable, their applicability is focused on legacy Parallel ATA systems. Vendors are increasingly releasing Serial ATA HDDs, and Serial ATA RAID controllers and HBAs as the standard´s adoption grows, and to meet the growing market demand as forward-looking users choose Serial ATA as their standard for the future.