SAS + SATA = The New Paradigm for Storage Efficiency

Authors: Chaz Nichols, Global Channel Marketing and Kent Bransford, Sr. Technical Editor
Seagate Technology

“The only constant is change” is surely a familiar (and vexing) maxim to storage managers around the world. Grappling with this ever-present challenge requires a storage interface capable of both meeting today’s requirements and seamlessly adapting as priorities inevitably evolve over time. Until recently, addressing an enterprise’s broad range of storage needs required a combination of SCSI and Serial ATA (SATA) infrastructures, an inefficient and unwieldy approach.

But now the rules have changed, thanks to Serial Attached SCSI (SAS) and its compatibility with SATA. A key component of the SAS feature suite, this ground-breaking compatibility produces remarkable storage synergies and efficiencies, enabling IT professionals to achieve their performance and capacity objectives with a single SAS infrastructure.

The one-two punch of the SAS/SATA value proposition is simple: SAS hard disk drives (HDDs) deliver the speed, reliability and scalability demanded in high-availability enterprise environments, while high-capacity SATA drives are purpose-built for bulk storage applications, combining low cost per GB and greater reliability and scalability than their parallel ATA ancestors.

The advantages of SAS/SATA compatibility benefit every sector of the storage landscape, from burgeoning firms with modest needs (and budgets to match) to vast Fortune 100 enterprises with a complex mix of transactional and reference data storage requirements.

No More Growing Pains
Smaller companies with limited resources can save money by deploying a SAS infrastructure (HBAs, backplanes, cabling, etc.) that is initially populated with low cost, high-capacity SATA HDDs. As business expands and greater capacity is needed, more SATA drives can easily be added. With far greater scalability than its SATA counterpart, a SAS infrastructure can connect over 16,000 SAS and/or SATA HDDs in one domain.

When these growing firms move further into online/transactional applications (entailing critical data with high availability to multiple, concurrent users), adding high-performance SAS drives is literally a snap, with zero modifications of the existing infrastructure required. Should storage priorities shift, it’s only a basic plug/unplug process to tweak the SAS/SATA drive mix within the SAS-based storage subsystem.

Prior to SAS, meeting these diverse storage objectives would have required deploying and maintaining two separate and distinct infrastructures (SCSI for transactional applications, SATA for bulk storage duties), a redundant and costly compromise for any company.

SAS, SATA & SFF: Best of All Worlds
Typically, more established enterprises already have extensive transactional (online) storage application needs, which they’ve historically addressed with parallel SCSI HDDs. SAS wisely leverages the acknowledged strengths of its parallel predecessor (rock-solid reliability, mature SCSI command set) while offering dramatic improvements in speed, scalability and compatibility.

Not surprisingly, savvy storage managers quickly recognized the many benefits of SAS HDDs over legacy parallel SCSI drives, and are transitioning to 3.5-inch (typically 15K RPM) SAS HDDs for online applications. As an added benefit, SAS enables these IT professionals to eliminate their current SATA infrastructures (deployed for bulk storage) and standardize on SAS infrastructure for both SAS and SATA HDDs, greatly simplifying management and maintenance duties.

But the advantages of SAS storage don’t end there. As noted earlier, a superior storage infrastructure must be able to adapt as needs change. It’s no secret that the enterprise is increasingly concerned with cutting space and power use in its data centers. For many forward-thinking enterprises, the answer can be found in the latest generation of space- and energy-efficient enterprise HDDs: small form factor (SFF) 2.5-inch 15K RPM drives.

SFF drives are leading the green revolution towards high-I/O-density storage solutions that facilitate rapid and cost-effective data center rationalization. SFF 2.5-inch 15K RPM drives are 70 percent smaller than conventional 3.5-inch 15K RPM drives, enabling them to use 30 percent less power and run cooler all while delivering 10 percent faster performance.

SAS is an ideal complement to SFF 2.5-inch 15K RPM drives, with its enormous scalability easily accommodating the greater drive counts found in high-density storage solutions. Furthermore, SAS helps maximize IOPS/U (Input Output Per Second/Unit), a metric that factors in both a storage device’s performance and its space requirements. SAS combines superior throughput with compact cabling and connectors that consume less enclosure space, enhancing airflow/cooling in high-density computing solutions such as 1U servers.

Speed, Capacity, or Efficiency: Pick Three
The real-world advantages of SFF SAS/SATA storage solutions are compelling: A 1U server using six 2.5-inch 15K SAS drives delivers full RAID 5 functionality in one-half the space required by a 2U server equipped with six 3.5-inch 15K RPM disk drives—and the SFF-equipped 1U server will boast faster performance.

What’s more, SAS/SATA compatibility enables a 1U SAS server to periodically migrate data off its SFF 15K SAS drives onto high-capacity SATA drives, thus freeing up more capacity for online/transactional applications. In short, SAS infrastructure can freely intermix 3.5-inch SATA drives with both 3.5-inch and SFF 2.5-inch SAS drives, thus maximizing storage efficiency by ensuring 1U SAS servers can effortlessly access both transactional and bulk storage.

SAS compatibility with SATA has set a lofty new standard for enterprise storage value, enabling transactional and bulk data storage to both reside in the same SAS infrastructure. And now the availability of SFF 15K SAS drives boosts the SAS/SATA value proposition even higher by spearheading the movement to more space- and energy-efficient storage solutions.

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