SCSI Library

SAS Advanced Connectivity

Advanced Connectivity » Definition

Serial Attached SCSI (SAS) burst upon the storage scene in 2004 as a serial replacement for the once ubiquitous parallel SCSI interconnect. While much attention is often given to the capabilities of the protocol and to the silicon and software required to implement these systems, it is often the physical interconnections that influence the adoption of I/O in a variety of market segments. Parallel SCSI, for example, supported everything necessary for clustered server deployments; however, the large unwieldy nature of the parallel cables and the restricted cabling distances greatly limited SCSI’s applicability in these markets.

 
SAS removed many of these restrictions by opening up the bandwidth, improving cabling distances, and providing a compact connection scheme suitable for today’s shrinking data center. While first generation solutions made tremendous strides forward, the connection schemes have continued to improve, opening up new markets for SAS in the process.

 
Below please find links to several useful documents that will help you learn about SAS Advanced Connectivity. Below the links, you will find a Frequently Asked Questions & accompanying answers.

 

sas-advanced-conn-roadmap-01-2012.jpg

12Gb/s 6Gb/s 3Gb/s

<!–SFF-8087 extends into SAS-3

  • The connector is 12G capable and some OEM’s prefer to keep their internal cabling the same for 12G that they had for 6G so they needed 8087 to be “approved” for use in SAS-3.

SFF-8088 extends into SAS-3

  • 8088 does not provide the cable management, the higher density or the 8x capability of 8644
    which were the reasons for redefining the interface for SAS-3 – therefore it would not be SAS-3 compliant – so it seems like the bars should be split up as shown above for the roadmap to be more correct.

 



 

 



 

SAS Advanced Connectivity Roadmap
Frequently Asked Questions

Q1. What is the Advanced Connectivity Roadmap?

A1. The Advanced Connectivity roadmap is STA’s connectivity roadmap to guide the industry through future SAS storage solutions. It specifies the Mini-SAS High Density (HD) (SFF- 8643/8644) connector as the converged connectivity scheme for SAS-based deployments and in addition, defines the SAS Connectivity Management scheme for simplifying cable and connectivity management.

 
Q2. Name the factors that stimulated provision of the Advanced SAS Connectivity Roadmap.

 
A2. Factors which drove provision of the Advanced SAS Connectivity Roadmap include simplification of cable and connector options and the provision of managed connectivity standards. Additional factors include providing high-density connectivity and the extension of active copper cable to 20m and optical cable to 100m.

 
Q3. What is a Mini-SAS High Density (HD) connector and how does it improve connectivity?
 
A3. The Mini-SAS HD connector doubles the port density over the Mini-SAS connector. Both internal and external solutions are available and it is electrically improved with less cross-talk and a much better signal-to-noise ratio. It supports active copper and optical cabling as well as SAS Connectivity Management.

 
Q4. What advantages result by extending copper cables to 20m or optical cables to 100m provide to SAS storage systems?

 

A4.
Longer cables enable more box-to-box, server-to-storage and rack-to-rack connections, thereby providing greater scalability (permitting accommodation of more spindles). Longer cables also allow greater configuration deployment flexibility.

 

Q5. In which external storage applications is 6Gb/s SAS now advancing dramatically?


 

A5.
Currently, 6Gb/s SAS has made significant advances in drive-attach and there is a growing opportunity for host-attached applications as well.

 

Q6. Will Advanced SAS Connectivity extend beyond 6Gb/s SAS?


 

A6.
Yes, it will be extended to 12Gb/s SAS when this next SAS generation enters the market.

 

Q7. What is SAS Connectivity Management?


 

A7.
SAS Connectivity Management is a consistent way of managing the cabling plan in any SAS system using the Mini-SAS HD connector. It is capable of detecting the presence or absence of a cable, number of SAS ports within the connector, what type of connection is being supported, (active, passive, optical), and other attributes important to storage system usability and serviceability.

 

Q8. What can Advanced SAS Connectivity contribute to cloud computing, large data centers and massive data enterprises?


 

A8.
Advanced SAS Connectivity provides greater distance, flexibility, scalability, serviceability and usability to large-size storage installations and uses.

 

Q9. What are the primary advantages of SAS Connectivity Management?


 

A9.
SAS Connectivity Management defines connectivity support including connection discovery and cable management; improved serviceability and usability without the need for mechanical keys; it also provides rapid fault isolation and minimal configuration errors; and last, it lowers Total Cost of Ownership (TCO).

 

Q10. In which SAS generation will SAS Connectivity Management appear?


 
A10. SAS Connectivity Management may be implemented rather quickly on the existing 6Gb/s SAS generation supported by the QSFP connector. While STA recognizes that some homogeneous deployments may use this connector, it is not the preferred connector for heterogeneous deployments. Mini-SAS HD systems are expected to take advantage of SAS Connectivity Management. These advantages will appear in the current 6Gb/s SAS generation, possibly in the first half of 2010. They will appear subsequently in the 12Gb/s SAS generation.