Data highways and SAS vs. SATA

• Data highways and SAS vs. SATA

With LSI’s recent announcement (in a press release on 25th July 2011) that the company has begun sampling 12Gb/s SAS technology to OEMs, it seemed a good time to write about SAS. Also an opportunity to clear up a couple common misconceptions.

SAS, or Serial Attached SCSI, is the current interface of choice in the enterprise for connecting drives (either HDDs or SSDs) to servers and storage arrays. Current technology is at 6Gb/s but 12Gb/s technology is just around the corner with plugfests occurring in 2012 and production hitting in 2013.

Good stuff – and double the speed too. Well…yes in a matter of speaking. And that’s the first area to clear up with misconception #1. With SAS speeds, we’re talking about bandwidth. An engineer many years ago explained it to me like this and I thought it was brilliant. He told me to think of SAS as if it was a highway system and the cars traveling on the highway represented the data from drives. When we move from generations, 6Gb/s to 12Gb/s for this example, it’s never really about how much faster the cars can go, but how much wider you make the roads so that more cars can travel on them before they are forced to slow down in “traffic”. And no doubt about it, with the growing amounts of data that we’re expected to see based on numerous industry forecasts, we need all the highway space we can get. And 12Gb/s technology will definitely provide more lanes on the road.

Misconception #2 relates to SATA vs. SAS and really covers a number of issues about how the technologies are often judged between each other. When having discussions with people over the years, there has been the general assumption that a SAS-based system should always be faster than SATA. Afterall, SAS is the traditionally preferred enterprise interface, costs more, and therefore should be superior in all ways right? The answer though is really dependent on the application and the environment where the storage is used. SAS has a lot more intelligence onboard, and a lot of it is related to maintaining data-integrity. Well that added intelligence means more functionality, which can relate to more time needed to complete some operations. A simple example is bootup – there’s more checking going on with a SAS system at bootup that a SATA system doesn’t do. So guess which will be faster? SATA.

But what about transactional performance? Again, depends on the system. Stick an otherwise equivalent single SAS drive into a workstation (Seagate Constellation and Constellation ES drives are offered with SATA or SAS), and the various error and data integrity checks can result in slightly slower performance. But if we’re talking a group of SAS drives in a server or storage array, then we’ll start to see great performance vs. what a group of SATA drives could otherwise do. SAS allows more customization of the system and many IT pros will configure their systems through adjusting mode page settings of the drives. For example, Seagate SAS drives like Constellation allow dual-porting, can be configured for enabling or disabling write cache, and customized for power management via four modes of PowerChoice settings.

So the bottom line is that a SAS-based system will shine when there are multiple drives running in a server or storage array, as well as providing protection for mission-critical data that SATA can’t offer. But for small systems where the extra functionality isn’t required, or single-drive environments for desktops and workstations, SATA is ideal. Each interface has its place.

Here is the press release of LSI on the 25th July 2011 :-


MILPITAS, Calif., July 25, 2011 – LSI Corporation (NYSE: LSI) today announced the industry's first sample shipments of 12Gb/s SAS RAID-on-Chip (ROC), controller and expander ICs to server and external storage OEMs, underscoring LSI® leadership in the SAS market segment. By providing customers with early samples of 12Gb/s SAS silicon, LSI is delivering a key technology milestone and laying the foundation for the anticipated SCSI Trade Association 12Gb/s SAS Plugfest in mid-2012.

Technology demonstrations for OEM customers showcase performance of over 1 million IOPS with a single 8-port 12Gb/s SAS ROC running small block sequential reads/writes in a direct connect configuration to eight hard disk drives.

"12Gb/s SAS technology will enable a new performance class of storage tiering that spans the enterprise from high-performance solid state storage to mega datacenter scale-out architectures,” said Dave Reinsel, group vice president, Storage and Semiconductors, IDC. “Early silicon availability is a critical first step toward 12Gb/s SAS infrastructure development, paving the way for a smooth technology transition and market adoption by late 2013.”

The 12Gb/s SAS generation will provide double the data transfer rate of 6Gb/s SAS solutions, allowing SAS infrastructure to deliver bandwidth that exceeds that of PCI Express® 3.0 with a single host bus adapter. The improved bandwidth, backed by I/O processing capabilities to maximize link utilization, supports increased scaling of traditional hard disk drives as well as improved solid-state drive (SSD) performance. 12Gb/s SAS will also provide customers with investment protection through designed backwards compatibility with 3Gb/s and 6Gb/s SAS infrastructures.

Along with these performance innovations are new connectivity options including new connectors and high-density cabling (Mini SAS HD) that features passive copper, active copper and optical capabilities, as well as enhanced cable management. These advancements, coupled with SAS expanders, which enable connection to a large numbers of devices, allow for new ways of scaling and configuring 12Gb/s SAS topologies. These topologies will extend the capabilities of SAS in direct attached storage environments for the public cloud and on-premise datacenter environments.

In the 12Gb/s generation, SAS expanders provide higher throughput and support higher port counts for both traditional hard disk drives as well as solid state storage. This improves storage consolidation for applications such as virtualization, tiered storage and digital content distribution.

“With more than 25 million SAS components shipped, and performance demonstrations of over one million IOPS from a single 12Gb/s SAS ROC, LSI is clearly a SAS market segment leader,” said Bill Wuertz, senior vice president, RAID Storage Division, LSI. "By offering our OEM customers sample shipments of the industry's first 12Gb/s SAS components, LSI is once again demonstrating its ability to keep our customers at the forefront of industry inflection points."

According to industry estimates, 12Gb/s SAS market adoption will begin with the release of individual SAS components and devices, and gain momentum as tier-one OEMs begin production-volume shipments of 12Gb/s SAS-enabled servers and external storage systems. Production-volume shipments of 12Gb/s SAS-enabled servers are estimated to occur by early 2013, followed by the availability of external storage systems by mid-to-late 2013.

Since the inception of SAS, LSI has delivered an industry-leading portfolio of products including SAS ROC, controller and expander ICs, host bus adapters, MegaRAID® and 3ware® RAID controllers, 6Gb/s SAS switches, advanced software options and WarpDrive™ SLP-300 acceleration cards. Based on a 25-year track record of hardware and firmware expertise and extensive validation processes, LSI is the SAS product supplier of choice for OEMs that want to deliver a broad set of storage solutions. Share this post on Data highways and SAS vs. SATA