Serial Storage Wire

6Gb/s SAS: What Is It and Why Do I Need It?

By Cameron T. Brett, Manager, Product Marketing,
PMC-Sierra, Inc.

You're an IT manager. You're job is to ensure the network, and more importantly the data, assuring it is always available. This is company-critical data: database transactions, records, E-mail and web operations. SCSI or SAS is the disk drive of choice because it's more reliable, faster and manageable in your IT framework. It works well, but you're always monitoring it closely.

6Gb/s SAS is coming in 2009. 6Gb/s SAS is the follow-on to 3Gb/s SAS and improves an already reliable and robust technology. Features have been added to the new SAS specification which enhances reliability, performance, manageability and security.

6Gb/s SAS Environment
The 6Gb/s SAS ecosystem is made up of several familiar devices. Controllers, sometimes referred to as initiators, are typically I/O or RAID-on-Chip (ROC) controllers embedded on the system motherboard or on a PCIe add-in card.

On the other end of the SAS link are disk drives and expanders. Expanders take a single SAS link and connect it to many disk drives and are typically used in servers and external storage arrays. SAS expanders are also used as switches, which connect any server to any disk array—similar to Ethernet or Fibre Channel switches.

Other SAS products include multi-port muxes, which allow a SAS controller to select between two outputs and disk drive multiplexers, allowing a single SAS/SATA disk drive to be connected to two SAS controllers. See Figure 1 for a comparison of 3Gb/s SAS and 6Gb/s SAS features.

Figure 1: SAS Features Evolve to Support Key Storage Trends

Improved Reliability and Manageability
The IT manager adventure continues – a disk drive in a storage array gets too many errors and begins to go off-line periodically. The storage array is one of five in a rack connected to servers and a SAN. It's managed through a management console in another room. New 6Gb/s SAS expanders can detect when the disk drive connection acquires too many errors and can send a message to the management console that the disk drive is having problems. It can be replaced before it fails – overnight when network use is low.

Managing SAS connections has become easier with 6Gb/s SAS. Technical improvements include better connectivity with SAS and SATA drives and for "hot plugging." SAS cabling has become more flexible with support for longer cables and a simplified connector scheme; only one type, not two, as it was with 3Gb/s SAS. (See Mini-SAS connectors below.)

Figure 2: Mini-SAS 4X Connectors

Increased Security
As business grows, more disk storage is needed and more servers are added. Whether they're tower, rack or blade servers, 6Gb/s SAS can control the access that each server has so only specific data can be accessed by certain servers. Secure zoning is a part of the new SAS-2 specification, specifically defined to increase security in a server and storage environment. A "zone" is similar to a hardware firewall that compartmentalizes a group of disk drives to create secure zones, segregating data. It works with 6Gb/s and 3Gb/s SAS and SATA disk drives within a 6Gb/s SAS environment.

Faster Performance and Investment Protection
Network user demands keep growing. More users mean more data and faster performance is necessary to keep up with demand. 6Gb/s SAS helps overcome the increased demands by doubling the throughput capability of SAS. Each SAS connection now supports up to 600MB/sec of throughput. Common SAS controllers come with four or eight ports, which creates connections up to 2.4Gb/s and 4.8Gb/s of throughput, respectively.

Moving to 6Gb/s SAS means faster data throughput yet it works with 3Gb/s SAS, which protects any current investment in SAS disk drives and storage systems. With the use of 6Gb/s SAS expanders, twice as many 3Gb/s disk drives can be connected with 6Gb/s SAS multiplexing capability.

And a little "green" too
The amount of performance per dollar increases as well with 6Gb/s SAS. As the cost of running a data center is directly related to power consumption, savings will come from higher performing storage at the same, or lower, power consumption. Fewer disk drives are needed to achieve performance targets with 6Gb/s SAS, which means less power and cost.

Summary
6Gb/s SAS is more than an improved set of features over the current generation of SAS. It offers IT managers highly tangible benefits that will make their data more reliable, secure and faster. Look for 6Gb/s SAS products and systems to make a significant impact on storage in 2009.

Cameron T. Brett
Manager, Product Marketing
Enterprise and Storage Division
PMC-Sierra, Inc.