Now, as SAS enters its second generation (6Gb/s SAS), the standard is evolving to meet the new demands of the modern data center which include server virtualization and high performance computing. The use case for SAS now goes well beyond a simple replacement for the obsolete parallel-bus architecture of SCSI. The standard now includes capabilities to improve bandwidth utilization, management and network robustness. While SAS is a major step forward in the evolution of storage it does not build from a blank page. Instead it builds on the decades of proven SCSI development and preserves its block protocol and command set. It also provides investment protection for the past as well as a transition to the future.

6Gb/s SAS builds on SAS-1’s legacy but also adds significant enhancements to its performance, networking capabilities and extends its overall reliability. These improvements continue to make straight SAS deployments a compelling alternative for the small to medium-sized enterprise.

Use Cases Overview

The most common deployment of SAS drives will be when installed in enterprise-class arrays. It is reasonable to expect that storage manufacturers will want to have their customers take advantage of 6Gb/s SAS hard drives and SSD drives which will be faster, just as reliable and less expensive than their fibre channel equivalents. SAS technologies will also provide a wider range of capacities and form factors for suppliers to choose from. The other use cases will be as internal drives or direct attached external arrays to servers that are not attached to network storage or as boot drives in servers that are. These systems will again benefit from the greater performance and reliability of the architecture.

There is also the use case of SAS drives as direct attached storage. This will be aided by a resurgence, of sorts, among application vendors where DAS is the recommended storage connection alternative, most noticeable in Microsoft Exchange 2010 deployments. This scenario was borne partly from a Microsoft directive to use local, but fast direct, attached storage and then have the application replicate that data to DAS on another server. Exchange 2010 has been re-tooled to fit this architecture and its goal is to allow the product to better compete with the inexpensive storage offered by Google’s Gmail. The impact is that Exchange 2010 environments may need to return to DAS and users may find that SAS-2 is the perfect candidate.

Where SAS and SAS-2 become particularly interesting though, is as a simple storage networking technology. Storage Switzerland calls this “Shared Direct Attached Storage” and it could be an area were SAS has the most significant impact. Initial storage networks are often built either to address capacity scaling issues for servers which have run out of internal expansion room, to handle smaller two- or three-node server clusters, or for server virtualization deployments so that advanced server virtualization features could be taken advantage of. It’s Storage Switzerland’s belief that networked SAS-2 may be an alternate method for customers to capture the benefits of virtual machine migration and mitigate server virtualization performance issues, all while keeping the simplicity of DAS.

What makes 6Gb/s SAS so compelling for these use cases is how well it excels at performance, connectivity and reliability while remaining affordable.

SAS-2 Primer White Paper../../../../SASWP.html

George Crump, Senior Analyst

To Download the complete SAS-2 Primer White Paper detailing SAS-2 Performance, SAS-2 Reliability, SAS-2 Networking and SAS-2 Deployment CLICK HERE

A White Paper by Storage Switzerland