Most organizations consider the data they capture daily to be their lifeblood. They also see it as an asset they must preserve for years—not only for legal, regulatory, due-diligence or compliance reasons, but mainly to extract value and intelligence and thereby enable better business decisions, improved organizational processes, advanced technologies and maximum profitability. To garner this value and intelligence, data must be easily accessible so the company can process it in real time, but also secure so it’s available later.
Users connect to data centers today in new ways, propelled by widespread availability of mobile devices. Extensive Internet use and data generated from photos, videos, audio streaming and social networking continue to grow exponentially. PCs, laptops, smartphones and tablets generate most of today’s data, but tomorrow’s data will come from connected and autonomous vehicles, factory robots and machine sensors, drones and surveillance systems, medical devices and wearable monitors, and more—creating a need for cloud-based data centers and efficient storage infrastructures.
Storage devices, such as solid-state drives (SSDs), hard-disk drives (HDDs) and tape drives, are widely deployed in data center servers and storage systems. To move data quickly, efficiently and reliably throughout the enterprise, devices based on Serial Attached SCSI (SAS) are an ideal choice. This point-to-point interconnect protocol transfers data serially, supports multipath I/O and delivers much faster data throughput than original parallel protocols. The interface, infrastructure and command set are well defined, robust and dependable.
The world’s top storage manufacturers continue to deploy flash-based SAS SSDs because SAS offers benefits and capabilities that differentiate it from other active storage protocols; the rumors of a SAS demise are greatly exaggerated.
SAS is a point-to-point serial storage-drive interconnect protocol that builds on the solid parallel SCSI interface it replaced in the mid-1980s. It’s the standard drive interface in storage apps today. The evolution of SAS has been driven by the amount of data that the protocol is specified to move successfully from one location to another, as Table 1 outlines. Next-generation SAS will have backward compatibility with SAS 2 and SAS 3 versions.
The SAS interface was developed and is maintained by the T10 technical committee of the International Committee for Information Technology Standards (INCITS).
Main Benefits of SAS
The SAS interface typically connects a host bus adapter (HBA) or redundant array of independent disks (RAID) card to a group of enterprise SSDs or HDDs, thereby collecting, preserving and protecting data while ensuring it’s available when needed. RAID can mirror data from one storage drive to another or spread it across multiple drives. If a power loss or system failure compromises a SAS drive, a new SAS drive can be plugged into the chassis next to the failed one. A RAID array copies data to a spare drive while the failed one is replaced. Data is then reassembled using RAID algorithms and parity data, rebuilding the new drive. This level of data redundancy is a major benefit to IT professionals.
A single SAS HBA card can support as many as 24 drives in a storage system using a combination of HDDs or SSDs. A SAS RAID card can support a similar number of drives, as well as numerous RAID levels for greater performance and data protection. By employing SSD performance with HDD capacity, data centers can make better use of storage resources.
The SAS protocol also supports high availability (HA) through dual-port capabilities, enabling two physical data paths in a single host. Two controllers can therefore access the same SAS drive simultaneously. If a data path is lost, the available data path continues operation as if no failure had occurred, creating minimal impact on quality of service (QoS). To support a 124 JBOD (just a bunch of disks) configuration using terabyte-capacity drives, using dual port and RAID is highly advisable. Only SAS drives deliver mature dual-port capability today.
If a SAS drive fails, the user can hot swap it to easily service this storage device without taking a node (server) offline. Additionally, since both HDDs and SSDs employ the same SAS interface, a user can easily combine SAS-based HDDs and SSDs in the same storage enclosure.
Power efficiency is yet another benefit of SAS-based storage devices. Some SAS SSDs feature selectable options that enable power consumption to be reduced if the performance requirement is lower. Users may sometimes be unable to take full advantage of SAS SSD performance in their storage systems; in these cases, the SAS protocol enables them to reduce power as well as the drive’s full performance potential. Western Digital, for example, supports 9W, 11W and 14W power options in its latest SAS-based Ultrastar SS300 SSD series.
Future Capabilities of SAS
One type of flash memory, 3D NAND, stacks the memory cells vertically, delivering greater storage density in the same physical footprint compared with 2D planar NAND architectures. In 2D NAND architectures, a U.2 (2.5-inch) form factor supports up to 8TB of storage capacity. In 3D NAND, the die size can be greater to enable future drive capacities of 60TB or more. From a performance perspective, the spaces between each memory cell in a 3D NAND architecture are wider than in 2D NAND, enabling storage devices to write data faster. The wider cell spaces also reduce noise and cell-to-cell interference from neighboring cells on the layer, delivering data with higher reliability.
As SSDs are reaching the performance capabilities of 12Gbps SAS, the industry is planning a next-generation rollout in which the next SAS Gen4 version will enable SSDs to deliver 24 Gbps of data throughput (expected in 2019/2020). This version will also be backward compatible with 6 Gbps Gen2 and 12 Gbps Gen3, protecting the customer’s initial SAS SSD investments.
IT departments must manage fast-growing data in their enterprises. Some have undertaken recent data center consolidation projects to reduce cost and power consumption while increasing performance, security and operational efficiencies. When evaluating their data access and storage challenges, infrastructures and devices based on SAS are well defined, stable, field proven and dependable. Driven by high bandwidth and proven enterprise capabilities, the SAS protocol will be relevant for at least another 10 years.
About the Author
Mitchell Abbey is the senior product-line manager for Western Digital Corporation’s enterprise-class solid-state drive (SSD) family. He’s responsible for driving and developing the enterprise business marketing plan as well as defining markets, products and features for the company’s high-performance solid-state storage products. Before Western Digital, Mitchell was a senior director of marketing and business development at Seagate. He also held senior positions at National Semiconductor and QformX. He has over 30 years of experience in business and product development, product-line management, and market analysis for a variety of technology products. Mitchell holds a Bachelor of Science degree in business administration and marketing from San Jose State University and two Associate of Engineering degrees in computer science and electrical engineering.