24G SAS (SAS-4)
Overview
24G SAS – The New Storage Backbone of the Data CenterThe demands of data storage and performance have increased tremendously since SCSI was developed 30 years ago. Replacing SCSI more than a decade ago, Serial Attached SCSI (SAS) is now the primary point-to-point serial protocol that is used to move data to and from computer storage devices such as Solid State Drives (SSDs), Hard Disk Drives (HDDs) and Tape drives. We have watched SAS transition over this time as performance demands continue to increase, doubling the performance of each new generation from the original 3 Gbps to 6 Gbps, on to the current generation of 12 Gbps. |
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The Need for New, Faster Storage Standard
The bandwidth offered by the current 12G SAS, defined at the physical layer by SAS-3, is well matched to the PCIe Gen 3 storage ecosystem.
However, the increase in computational workloads and storage traffic is driving the industry to faster CPU and storage interconnect via PCIe Gen 4. 24G SAS, defined at the physical layer by SAS-4, is a new storage standard that was created to meet the performance needs of the PCIe Gen 4 ecosystem. It supports data rates of 22.5 Gbps which doubles the data throughput of the previous generation SAS-3 standard, eliminating storage bottlenecks to SSDs and HDDs in the data center.
What is Different About the New 24G SAS Specification?
24G SAS technology is more than a speed upgrade for Serial Attached SCSI interface. This new standard implements a major overhaul of the interface, including the use of the all-new 128b/150b encoding, with 20-bit Forward Error Correction, as well as a number of other new features and enhancements. The new SPL packet encoding scheme also introduces the opportunity for new bandwidth aggregation techniques. The existing SAS value proposition of reliability, availability, scalability, flexibility, and low total cost of ownership is preserved. In addition, SAS-4 technology will maintain backwards compatibility with previous-generation SAS implementations, which means that older drives will be compatible with newer storage controller and SAS expander products.
24G SAS Features
- Double the effective storage bandwidth from 1.2GBps per lane to 2.4GBps per lane
- Backwards compatibility with SAS-3 (12 Gbps), SAS-2 (6 Gbps) and SATA (6 Gbps)
- Preserves the existing SAS value proposition of reliability, availability, scalability, flexibility, and low cost
- Protects your storage investment
Dynamic Channel Multiplexing (DCM)
24G SAS with Microsemi Dynamic Channel Multiplexing (DCM) removes bottlenecks in storage infrastructure even when utilizing SATA and SAS-3 drives, enabling greater performance and ultimately better storage utilization in the data center.
Dynamic channel multiplexing (DCM) technology enables storage subsystems to harness the full performance capabilities of PCIe Gen 4 enabled systems by enabling extremely efficient aggregation of transactions to lower speed drives (6G and 12G). Fully interoperable with existing SAS and SATA infrastructure, DCM can extend the lifecycle of legacy rackmount storage by aggregating throughput within the SAS fabric.
Microsemi has collaborated with Teledyne LeCroy to develop test tools for DCM, ensuring our partners can efficiently deploy this innovative technology. With the introduction of the first 24G SAS analyzer, jammer and exerciser system, Teledyne LeCroy has now assembled the most complete line of protocol layer test tools for storage vendors targeting 24G SAS development.
Who will Benefit from the new 24G SAS?
The need for increased storage performance affects organizations across practically every industry, including hyperscale data center, banking, education, government, healthcare and manufacturing. All data centers will continue to require SAS or SATA media, whether that be SSDs or HDDs, for mission-critical data. As the industry transitions to PCIe Gen 4, SAS-4 will become increasingly relevant to ensure that the CPUs are not starved for storage bandwidth to the ever increasing TeraBytes of stored user data.
Are SAS-4 Drives Required To Take Advantage of 24G SAS?
No, they are not. 24G SAS offers the required bandwidth aggregation of lower speed drives (be they 6G SATA, 6G SAS, or 12G SAS) to fully utilize the PCIe Gen 4 uplink from the storage controller to the CPU.
Where to next?
Host bus adapters (HBAs) and IOCs, RAID adapters and controllers (ROCs), and expanders supporting the new SAS-4 technology are sampling now.
24G SAS Demo
Microchip demonstrates how their SmartRoC 3200 storage controllers and SXP 24G SAS expanders, along with Dynamic Channel Multiplexing (DCM) technology, eliminates bottlenecks at the CPU host interface and allows more efficient use of legacy storage infrastructure.
Press
August 6, 2018
Microsemi Leading Industry Innovation with 24G SAS and PCIe Gen 4 Tri-mode Storage Controller Technology
16 Nanometer Controllers Will Unleash the Full Potential of Storage Infrastructure Technologies for the PCIe Gen 4 Data Center
August 7, 2018
Microsemi Announces Industry's First 24G SAS Expanders for Data Center Storage
New Family Addresses High Bandwidth Storage Needs to Unlock Full Performance Capabilities of PCIe Gen 4-Capable Systems