Serial Attached SCSI – FAQ
- What is Serial Attached SCSI (SAS)?
- Why do I need SAS?
- How does Serial Attached SCSI benefit the storage industry?
- What are the end user benefits of Serial Attached SCSI?
- Are Serial Attached SCSI connectors compatible with those of current SCSI server and storage solutions?
- Is Serial Attached SCSI complementary to Serial ATA?
- Can I use Serial Attached SCSI hard disk drives in my Serial ATA workstation or desktop PC?
- Where can I find more information on Fujitsu hard disk drive technology?
- How can I get more information on Serial Attached SCSI? What other companies support the move to SAS?
- What is 6Gb/s SAS?
- What is the distinction between 6Gb/s SAS and the SAS-2 specification?
- What new features does 6Gb/s SAS bring to Serial Attached SCSI (SAS)?
- What new benefits will 6Gb/s SAS bring to the enterprise storage market?
- What is multiplexing and how does 6Gb/s SAS utilize the capability?
- Does 6Gb/s SAS have zoning enhancements beyond the 3Gb/s SAS generation?
- Does 6Gb/s SAS retain SMP functionality?
- Will 6Gb/s SAS be backward compatible with 3Gb/s SAS? If so, how?
- What other connectivity features can be found in 6Gb/s SAS?
- What are the benefits of self-configuring expanders?
- What is the 6Gb/s SAS deployment time-line?
- How will 6Gb/s SAS component costs compare to 3Gb/s SAS?
General SAS Questions
Q: What is Serial Attached SCSI (SAS)?
A: Serial Attached SCSI (SAS) is the logical evolution that satisfies the enterprise data center requirement of scalability, performance, reliability and manageability, while leveraging a common electrical and physical connection interface with Serial ATA (SATA). This compatibility provides users with unprecedented choices for server and storage subsystem deployment.
Q: Why do I need SAS?
A: SAS was developed to address anticipated input/output (I/O) and direct attach storage requirements in the future. It provides universal interconnect with SATA, while offering logical SCSI compatibility along with SCSI reliability, performance and manageability.
Q: How does Serial Attached SCSI benefit the storage industry?
A: SAS leverages the proven SCSI technologies that customers expect in data center environments, providing robust solutions and generational consistency. It is based on a serial interface, allowing for increased device support and bandwidth scalability, and reducing the overhead impact that challenges today's SCSI environments. It utilizes SATA development work on smaller cable connectors, providing customers a downstream compatibility with desktop class ATA technologies. Simplified routing will enable a new generation of dense devices, such as small form factor hard disk drives, enabling storage solutions to scale externally.
Q: What are the end user benefits of Serial Attached SCSI?
A: Key end user benefits include enterprise class robustness, investment protection in compatible SCSI software and middleware and the choice of direct-attach storage devices (SAS or SATA). In addition, longer cabling distances, smaller form factors and greater addressability will all lead to a new level of flexibility when deploying mainstream data center servers and subsystems. Since SAS is based on the foundation of the industry-leading SCSI specification, reliability and peace of mind will satisfy user's needs for continuity in the data center.
Q: Are Serial Attached SCSI connectors compatible with those of current SCSI server and storage solutions?
A: No, SAS connectors differ from current SCSI connectors. They are much smaller.
Q: Is Serial Attached SCSI complementary to Serial ATA?
A: SAS complements SATA by adding dual porting, full duplex, device addressing and it offers higher reliability, performance and data availability services, as well as logical SCSI compatibility. It will continue to enhance these metrics as the specification evolves, including increased device support and longer cabling distances. SATA is targeted to cost-sensitive non-mission-critical desktop storage environments. Most importantly, these are complementary technologies based on a universal interconnect, where SAS customers can choose to deploy cost-effective SATA drives in a SAS storage environment.
Q: Can I use Serial Attached SCSI hard disk drives in my Serial ATA workstation or desktop PC?
A: SAS hard disk drives can be used on desktops and workstations by adding a host bus adapter.
Q: Where can I find more information on Fujitsu hard disk drive technology?
A: More information about Fujitsu hard disk drives can be found at us.fujitsu.com/hdd.
Q: How can I get more information on Serial Attached SCSI? What other companies support the move to SAS?
A: More information can be found at http://www.scsita.org. In addition, this site includes a list of supporting companies.
Q: What is 6Gb/s SAS?
A: 6Gb/s SAS is the marketing name that the SCSI Trade Association (STA) has given to the industry standard based on the SAS-2 specification. It is the next generation of the SAS protocol beyond the current 3Gb/s SAS. One of the key benefits of SAS is its commonality with the Serial ATA (SATA) electrical and physical connection interface to help improve system cooling and lower system cost. With enterprise storage requirements constantly changing and becoming more complex, factors such as larger capacity, greater density and scalability are more critical than ever. SAS was conceived to meet these demands while providing the highest performance. The first and current generation of SAS is a 3Gb/s offering which takes advantage of features such as dual-ported drives, wide ports and full duplex transmission to provide a performance advantage over parallel SCSI. 6Gb/s SAS will build upon this performance heritage by doubling the amount of available bandwidth for enterprise applications.
Q: What is the distinction between 6Gb/s SAS and the SAS-2 specification?
A: SAS-2 is the name of the latest SAS specification going through the T10 Technical Committee process. In SAS-2, 6Gb/s signaling is a component of the overall specification. It specifies all of the new features being incorporated into the new technology as well as how to implement these features (i.e., multiplexing). 6Gb/s SAS is the industry standard based on the SAS-2 specification and defines a short list of features that must be supported. Products labeled 6Gb/s SAS have, as a minimum, the following features (if applicable, according to product type): 6Gb/s transfers, external Mini-SAS connectors, SSC, DFE, Standardized Expander Zoning, self-discovering expanders, and (optionally) multiplexing. STA is supporting and endorsing the aforementioned list of features for 6Gb/s SAS products.
Q: What new features does 6Gb/s SAS bring to Serial Attached SCSI (SAS)?
A: The 6Gb/s SAS transfer rate doubles system throughput over 3Gb/s SAS. For example, using SAS as the connection between a host and an external storage controller, a wide (x4) SAS channel enables data transfers of 24Gb/s in both directions (full duplex).
Q: What new benefits will 6Gb/s SAS bring to the enterprise storage market?
A: i.) 6Gb/s SAS will improve signal conditioning and integrity through Decision Feedback Equalization (DFE). Signal integrity will be improved over existing 6-meter SAS cables and enable the utilization of 10-meter cables in 6Gb/s SAS environments, thus expanding connectivity options.
ii.) Spread Spectrum Clocking (SSC) reduces Electromagnetic Interference (EMI) failures. SSC is not required for 3Gb/s SAS connections.
iii.) RAS (Reliability, Availability & Serviceability) enhancements include physical improvements, enhanced zoning and improved symmetric multi-processing (SMP) functionality.
Q: What is multiplexing and how does 6Gb/s SAS utilize the capability?
A: Multiplexing (also know as Time Division Multiplexing, or TDM) optimizes 3Gb/s SAS infrastructure. It allows multiple 3Gb/s devices to share 6Gb/s SAS bandwidth. For example, an expander can multiplex two 3Gb/s device data streams (to fully utilize the 6Gb/s bandwidth) to an upstream port. Multiplexing will enable 6Gb/s SAS to connect to 3Gb/s SATA drives, providing a smooth transition from 3 to 6Gb/s data transfer speeds. Note: Multiplexing must conform to the SAS–2 specification definition.
Q: Does 6Gb/s SAS have zoning enhancements beyond the 3Gb/s SAS generation?
A: Yes, enhanced zoning allows configuration to take place in parallel, downstream of expanders, enabling the ability to keep poorly functioning devices, or devices that are down, from being exposed to the storage infrastructure. This also increases system boot speeds because of parallel discovery processes.
Q: Does 6Gb/s SAS retain SMP functionality?
A: 6Gb/s SAS has improved SCSI Management Protocol (SMP) functionality, enabling improved communication and diagnostics in the SAS infrastructure, allowing for improved error reporting and fault isolation.
Q: Will 6Gb/s SAS be backward compatible with 3Gb/s SAS? If so, how?
A: Yes, a 6Gb/s SAS objective is to maintain compatibility with existing SCSI software and middleware. In addition, it is compatible with the hardware in existing SAS installations. Electrical protocols, cables and mini-SAS connectors (4x & 4i) are all compatible with previous generations. Generational backward compatibility provides investment protection.
Q: What other connectivity features can be found in 6Gb/s SAS?
A: Use of equalization with 6Gb/s SAS signaling permits longer cables than 3Gb/s SAS. Port selectors will likely be required for systems connecting 6Gb/s SATA drives (when they become available) into 6Gb/s SAS systems.
SAS also has potential as a fabric with the use of expenders to create a vast network.
Q: What are the benefits of self-configuring expanders?
A: They promote richer SAS topologies and improve SAS discovery times, including standardized zoning expanded to 256 devices. Discovery is executed by SAS expanders, all of which reduces time to discover large topologies, enabling zoning of the topology and table-to-table routing.
Q: What is the 6Gb/s SAS deployment time-line?
A: 6Gb/s SAS prototypes were introduced to the market as early as 3Q07. The first 6Gb/s SAS plugfest will be held in 4Q08. Initial components such as HBAs and backplanes will start to roll out in 1H08, with production components out in 2H08. Storage systems, such as servers and external storage, will begin shipping in 2009.
Q: How will 6Gb/s SAS component costs compare to 3Gb/s SAS?
A: It is anticipated that the cost of 6Gb/s SAS components will remain in line with the costs of 3Gb/s components as they enter the market. With the SAS market growing at a rapid rate, there is little indication that future SAS component costs will be higher than current costs.
